CN115728250B - Semiconductor carrier dynamics test instrument and test method - Google Patents

Abstract

The invention discloses a semiconductor carrier dynamics test instrument and a test method, wherein the semiconductor carrier dynamics test method comprises the following steps: placing a semiconductor sample in a microwave resonant cavity; providing continuous excitation light to excite the semiconductor sample to generate carriers, and providing steady-state bias background light to fill defect states of the semiconductor; a microwave analyzer is adopted as a microwave source and a detector to detect the microwave signal of the semiconductor, so as to obtain a time-resolved microwave photoconductive curve; carrying out frequency sweep of the whole frequency band on the microwave signal to obtain a time resolution microwave spectrum; and acquiring semiconductor carrier dynamics information according to the time-resolved microwave spectrum. The test method can effectively distinguish different carrier dynamics processes caused by carrier radiation recombination and defect capture.

Description

A semiconductor carrier dynamics test instrument and test method

Technical Field

The present invention relates to the technical field of semiconductor material detection, and in particular to a semiconductor carrier dynamics testing instrument and a testing method.

Background Art

In recent years, with the rapid development of information technology and microelectronics, people's demand for semiconductor materials and semiconductor devices has also increased year by year. In practical applications, engineering and technical personnel often need to test the quality of semiconductor wafers. The previous sampling inspection method is often inefficient and costly. Conventional electrical performance tests and optical performance tests are relatively independent. For example, reflection, absorption and fluorescence spectra are used to characterize the absorption factor, refractive index and band gap of semiconductor materials. The conductivity, carrier mobility and carrier concentration of semiconductor materials are tested using the four-probe method and the Hall effect. The dielectric properties of materials at different frequencies are tested using an LCR meter. However, these conventional tests can only obtain relatively basic information, and the tests are complicated and require the use of various instruments. In addition, for the photoelectric performance test of semiconductor materials, especially the test of carrier dynamics (including important parameters such as carrier lifetime and mobility).

Charge carrier dynamics are studied by time-resolved photoluminescence (TRPL). Once a semiconductor is excited by a pulsed laser, it spontaneously generates charge carriers that can recombine with each other in either a radiative or non-radiative manner. However, TRPL decays can only reflect radiative processes. If a comprehensive understanding of the charge recombination of the entire charge carriers is required, non-radiative recombination losses must also be determined. For most efficient lead-based perovskites, the recombination losses can indeed be dominated by the radiative part. Therefore, the lifetime determined by TRPL is more or less representative of their optoelectronic properties and can be closely related to the device performance. However, recently developed 2D/3D perovskites, tin-based perovskites, and additive-enhanced perovskites show ultra-long carrier lifetimes determined by time-resolved microwave conductivity (TRMC) tests. In principle, if non-radiative losses are negligible, the TRMC decay should overlap with the TRPL decay. However, if shallow traps in the sample induce additional charge trapping and de-trapping processes, the charge carrier decay after photoexcitation can be more complicated, and additional techniques are needed to characterize these non-radiative recombination losses.

At present, the mainstream charge carrier dynamics test technology on the market is transient fluorescence spectroscopy (TRPL), and there are also a small number of time-resolved microwave photoconductivity (TRMC) and transient terahertz spectroscopy (OPTP) imported from abroad. However, these high-end instruments are generally expensive, with a low market share, and cumbersome operation and maintenance. They have high technical requirements for experimental personnel and require a good theoretical and experimental foundation for both the optical path and the electrical measurement system. In addition, the functions of the commercial transient photoelectric analysis and characterization systems on the market are still relatively simple. For example, transient fluorescence spectroscopy can only test and characterize radiation recombination losses, and traditional time-resolved microwave photoconductivity technology lacks effective means to distinguish the complex dynamics caused by different defect energy levels. Among them, although time-resolved microwave photoconductivity technology has been well applied in the characterization of semiconductor mobility, the current technology mainly uses ultrafast nanosecond lasers to excite semiconductors, and then uses single-point microwave sources and microwave detectors to detect changes in carrier concentration in semiconductors, thereby correlating carrier concentration with microwave transmittance/reflectivity. However, the current mainstream TRMC technology still has many shortcomings, such as the inability to distinguish the carrier mobility of holes and electrons separately, and the measured value is a comprehensive mobility value. In addition, although the current TRMC technology also uses white light background, it is limited by single-point microwave detection and has not yet been able to scan the entire frequency band to obtain the time-resolved spectrum of the entire band, which is particularly important for the study of carrier defects in semiconductors. In summary, there is still a lack of small, easy-to-operate, and powerful carrier dynamics analysis instruments on the market, especially effective means to analyze carrier mobility, lifetime, and complex dynamics caused by defect capture.

Summary of the invention

The first purpose of the present application is to provide a semiconductor carrier dynamics testing method, which is a technology that uses optical pumping-microwave detection, and additionally adds steady-state bias light to selectively fill the defect states of the semiconductor. By scanning the time-resolved spectrum of the microwave signal, different types of carrier dynamics processes in the semiconductor can be effectively distinguished.

The second object of the present application is to provide a semiconductor carrier dynamics testing instrument.

The technical solutions provided by this application are as follows:

A semiconductor carrier dynamics testing method, comprising:

Placing a semiconductor sample in a microwave resonant cavity;

Providing continuous excitation light to excite semiconductor samples to generate carriers, while providing steady-state bias background light to fill defect states in the semiconductor;

A microwave analyzer is used as a microwave source and detector to detect the microwave signal of the semiconductor and obtain the time-resolved microwave photoconductivity curve;

Sweep the microwave signal across the entire frequency band to obtain a time-resolved microwave spectrum;

Obtain semiconductor carrier dynamics information from time-resolved microwave spectroscopy.

On the basis of the above technical solution, by changing different bias background light intensities and irradiation wavelengths, a set of time-resolved microwave photoconductivity curves are obtained, and the time-resolved microwave spectra of the set of time-resolved microwave photoconductivity curves are fitted to obtain carrier dynamics information.

On the basis of the above technical scheme, the intensity and irradiation wavelength of different bias background light are changed to obtain the time-resolved microwave photoconductivity curves under different defect filling states. According to the changes in amplitude and frequency, the change in cavity Q value or microwave reflectivity is calculated, and the microwave complex conductivity characteristics of semiconductor samples in steady state and excited state are analyzed.

Based on the above technical solution, the phase of the time-resolved microwave spectrum corresponds to the imaginary part of the semiconductor dielectric constant, which is used to analyze the dynamics of deep energy level defect capture; the amplitude information of the time-resolved microwave spectrum corresponds to the real part of the semiconductor dielectric constant, which is used to analyze the carrier light generation rate and the dynamics caused by shallow energy level defect capture.

On the basis of the above technical solution, analyzing semiconductor carrier dynamics according to time-resolved microwave spectra includes: fitting different time-resolved microwave spectra and analyzing the energy level and density of semiconductor defects.

On the basis of the above technical solution, the method also includes: detecting the attenuation of the microwave signal under different time delays and recording the dynamic process of carriers in the semiconductor sample.

On the basis of the above technical solution, the method further comprises:

Compare different time-resolved microwave spectra, analyze the changes in phase and amplitude information in microwave signals, and distinguish different types of carrier dynamics processes in semiconductors.

The semiconductor carrier dynamics testing instrument provided in this application includes:

An excitation light source, which is used to provide pulsed excitation light to the semiconductor sample to excite the semiconductor sample to generate photogenerated carriers;

A background light source, which is used to provide biased background light of different light intensities to the semiconductor sample to fill different defect states of the semiconductor sample;

A microwave analyzer, which acts as a microwave source and detector, is used to acquire a time-resolved microwave spectrum.

On the basis of the above technical solution, the semiconductor carrier dynamics test instrument further includes:

a spectrometer for recording steady-state photoluminescence spectra;

A time-correlated single photon counter is used to acquire time-resolved photoluminescence spectra.

On the basis of the above technical solution, the semiconductor carrier dynamics test instrument also includes:

A fiber coupler, used for coupling the pulsed excitation light and the biased background light to one optical fiber; and

The optical mixer is used to receive the pulse excitation light and the bias background light transmitted by the optical fiber and mix the two.

On the basis of the above technical solution, the pulse repetition frequency, laser power density and wavelength of the excitation light source are continuously adjustable. Further, the pulse repetition frequency of the excitation light source is continuously adjustable between 1Hz and 1kHz, and the laser power density is continuously adjustable between 100nJ/ ^cm2 and 100μJ/ ^cm2 ; the pulse width of the pulse excitation light is between 20fs and 20ns, and the wavelength is between 190nm and 2400nm.

On the basis of the above technical solution, the intensity and wavelength of the biased background light are adjustable. Further, the intensity of the biased background light is continuously adjustable between 0 and 100 mW/ ^cm2 , and the wavelength is continuously adjustable between 400 nm and 3500 nm.

Based on the above technical solution, the frequency band of the microwave source is continuously adjustable. Further, the frequency band of the microwave source is continuously adjustable between 1 GHz and 18 GHz, and the time resolution of microwave emission and reception is 5 ns to 10 ns.

The present invention has the following advantages and beneficial effects:

(1) The present invention adopts non-contact optical testing technology, which can directly test the electrical properties of semiconductor thin film samples, including carrier mobility, lifetime, dielectric constant and complex conductivity.

(2) The present invention can effectively distinguish and fill defect states through background light bias, and study the influence of defect states on semiconductor carrier dynamics.

(3) The present invention utilizes the analysis of microwave spectrum changes to effectively study the complex conductivity and complex dielectric constant of semiconductor materials and distinguish the effects of different defect energy levels on semiconductor carrier dynamics.

(4) The present invention can study different types of semiconductor materials, including silicon, gallium arsenide, gallium nitride, hybrid perovskite, organic semiconductors and chalcogenide semiconductors, by regulating the microwave cavity and light excitation conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further described below with reference to the accompanying drawings, but the embodiments in the accompanying drawings do not constitute any limitation to the present invention.

FIG1 is a schematic diagram of a semiconductor carrier dynamics testing instrument used in various embodiments;

FIG2 is a time-resolved microwave photoconductivity spectrum of the gallium nitride film in Example 1;

FIG3 is a time-resolved microwave photoconductivity curve of the gallium nitride thin film sample of Example 1;

FIG4 is a time-resolved microwave photoconductivity curve of different perovskite films in Example 2;

FIG5 is a time-resolved microwave photoconductivity curve of perovskite with different sodium ion doping concentrations in Example 2;

FIG6 is a time-resolved microwave photoconductivity curve under different bias background lights in Example 3;

FIG7 is a two-dimensional TRMC spectrum without bias background light (a) and with bias background light (b) in Example 3;

FIG8 is a time-resolved microwave photoconductivity curve of different inorganic semiconductor materials in Example 4.

DETAILED DESCRIPTION

In order to make the present invention easier to understand, specific embodiments of the present invention will be further described below.

As shown in FIG1 , the semiconductor carrier dynamics testing instrument provided in the present application includes an excitation light source, a background light source, a spectrometer, a time-correlated single photon counter, a microwave resonant cavity, and a microwave analyzer.

The excitation light source can be a pulsed laser or an ultrafast pulsed light emitting diode, the excitation light pulse width is between 20fs and 20ns, the excitation light intensity can be continuously adjustable, and its intensity is between 100nJ/ ^cm2 and 100μJ/ ^cm2 . The wavelength of the excitation light can also be adjusted between 190nm and 2400nm, and the wavelength of the excitation light depends on the band gap of the semiconductor material. The pulse repetition frequency of the excitation light source is adjustable between 1Hz and 1kHz. The present application adopts an OPO wavelength tunable laser, which has a pulse energy of >5mJ, a pulse width of 7ns, a pulse repetition frequency of 10Hz, and can be easily attenuated and tuned.

The background light source is preferably a white light source, for example, a halogen tungsten lamp is used as a continuous light excitation source to perform background irradiation on the sample. The intensity of the white light bias can also be adjusted between 0 and 100 mW/ ^cm2 , and the wavelength range is 400nm to 3500nm. The white light bias can well fill the internal defects of the semiconductor material. The white light and pulse excitation light source are coupled to an optical fiber through a fiber coupler, and the other end is connected to a mixer and directly irradiated to the sample. In this way, the light source after mixing is more uniform, which can reduce experimental errors. By testing different background light bias intensities and irradiation wavelengths, a set of TRMC kinetic curves can be obtained, and then the TRMC time-resolved spectrum is fitted to obtain carrier dynamics information.

After the excitation light is irradiated onto the semiconductor sample, photogenerated carriers are generated. The thermal motion of these excess carriers can well absorb and reflect the microwaves emitted by the microwave source. Here, the microwave source uses a 1GHz to 18GHz swept frequency microwave source to replace the traditional single-frequency point source, thereby obtaining a time-resolved spectrum change with more sample information. The time resolution of microwave emission and reception is 5ns to 10ns; specifically, the present application uses a FieldFox handheld microwave analyzer (Keysight, N9915A) as a microwave source and detector.

The semiconductor sample used in this application is a thin film sample, which is placed in a microwave resonant cavity. The time-resolved microwave photoconductivity test is divided into two modes: transmission and reflection. In the transmission mode, the thickness of the thin film sample is between 10nm and 10μm. The reflection mode has no requirements for the film thickness and can be tested on the surface of millimeter-level wafers or single crystal particles.

By testing the changes in the amplitude and frequency of the resonant peak in the microwave cavity, the changes in characteristic parameters such as the cavity Q value and microwave reflectivity can be effectively analyzed, thereby further analyzing the microwave complex conductivity characteristics of semiconductor materials in the steady state and excited state. In addition, by detecting the attenuation of microwave signals under different time delays, the dynamic process of carriers in semiconductor samples can also be recorded.

By adopting the above technical scheme, the present invention can effectively test and analyze the carrier dynamics of semiconductor materials, and can specifically study the influence of different defect states on their dynamics.

Steady-state photoluminescence (PL) spectra were recorded using a Morpho-Nova spectrometer under excitation with a 450 nm continuous laser. Time-resolved photoluminescence spectra (TRPL) were obtained using the time-correlated single photon counting technique TimeHarp 260PICO single, PicoQuant GmbH). Using a picosecond diode laser (405 nm, PiL040X) as the excitation light source, the charge carrier mobility was characterized by time-resolved microwave conductivity (TRMC) measurements, which is an electrode-free technique and can effectively probe the carrier dynamics of semiconductors. The change in microwave power (ΔP/P) during the measurement was monitored by the cavity reflecting the 530 nm laser upon sample excitation and correlated to the photoinduced change in the sample conductivity:

where ΔG is the change in conductivity, ΔP(t)/P is the change in detected microwave power, and K is the sensitivity factor of the cavity, which depends on the size of the cavity, the quality of the cavity walls, and the dielectric properties of the semiconductor sample in the cavity.

The change in photoconductivity ΔG is related to the quantum yield of charge carrier generation and the sum of the hole μ _h and electron mobility μ _e , ∑μ = μ _e + μ _h ,

where β is the ratio between the wide and narrow inner dimensions of the waveguide, _FA is defined in optical measurements to determine the fraction of converted photons, _FA = 1-( _FR + _FT ), where _FR and _FT are the fraction of light reflected and transmitted by the perovskite film, respectively, _I0 is the excitation light intensity, and e is the unit charge.

The following examples use the above-mentioned semiconductor carrier dynamics testing instrument to test various semiconductor samples. Unless otherwise specified, the semiconductor samples are commercially available products or obtained by conventional preparation methods, and the data and spectrum acquisition and processing methods all use common technical means in the field.

Example 1

We used the semiconductor carrier dynamics test instrument mentioned above to study the third-generation wide-bandgap semiconductor gallium nitride film. The principle of TRMC is shown in Figure 1. The white light background is optional and is mainly used to study the influence of shallow energy level defects. The excitation light wavelength used here is a 250nm ultraviolet pulse laser with a pulse width of 5ns and a pulse repetition frequency of 10Hz.

Figure 2 is a typical TRMC spectrum of a GaN film in a microwave cavity. By fitting this spectrum, the Q value and reflectivity of the microwave cavity can be well obtained.

Figure 3 shows the TRMC kinetic curves of GaN films excited at different laser intensities. It can be seen that with the increase of excitation intensity, the carrier microwave lifetime decreases, but it is still at a large value, up to milliseconds. The epitaxially grown GaN film also has an extremely high mobility (~5000cm ² V ^-1 s ^-1 ).

Example 2

The semiconductor carrier dynamics test instrument and test method of this embodiment tested different perovskite films prepared by the solution method, as shown in Figure 4. The excitation light source used in the test is a 532nm nanosecond laser with a pulse width of 8ns and a pulse repetition frequency of 5Hz. It can be seen that the three perovskites have different carrier dynamics processes. For example, the most classic methylamine lead iodine ( _MAPbI3 ) semiconductor has the shortest lifetime, which is only a few hundred nanoseconds, while the ternary perovskites (MAFACs) that have been studied more in recent years have a longer carrier lifetime, which can reach several microns, and the ternary perovskites (2D/3D) treated with the two-position perovskite PEAI have the least defect states and the longest carrier lifetime. These carrier dynamics information is also inseparable from the performance improvement of perovskite solar cells in recent years.

Figure 5 compares the effects of typical two-dimensional perovskites (FACs) and different concentrations of sodium ion doping on their carrier dynamics. It can be seen that with the increase of sodium ion concentration, the carrier lifetime is significantly improved.

Example 3

Although Example 2 observed an ultra-long carrier lifetime in the perovskite film, the cause of this lifetime is still uncertain. This example continues to introduce white light bias based on the ordinary TRMC technology, and the white light intensity is between 0 and 1000 μW/cm ² , as shown in Figure 6, and Figures 7a and 7b are two-dimensional TRMC spectra without background irradiation and with background irradiation bias, respectively. It can be seen that with the increase of the white light bias intensity, the carrier lifetime in the doped perovskite film gradually decreases, which shows that the carrier defects in the film can be well filled by the carriers generated by white light, and there is no process of shallow energy level defects to capture and release carriers, and there is no ultra-long lifetime.

Example 4

In this embodiment, several conventional semiconductor films, including gallium arsenide, indium phosphide and indium gallium arsenide, are tested using the semiconductor carrier dynamics test instrument and test method. The excitation wavelength is 630nm, the laser pulse width is 8ns, and the pulse repetition frequency is 10Hz. The carrier dynamics are shown in FIG8. It can be seen that both gallium arsenide and indium phosphide have extremely high carrier mobility and lifetime (>1000cm ² V ^-1 s ^-1 ), while indium gallium arsenide has lower mobility and carrier lifetime.

The above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principle of the present invention, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims (8)

1. A semiconductor carrier dynamics testing method, comprising:

Placing a semiconductor sample in a microwave resonant cavity;

providing continuous excitation light to excite a semiconductor sample to generate carriers, and simultaneously providing steady-state bias background light with different light intensities to fill defect states of the semiconductor;

A microwave analyzer is adopted as a microwave source and a detector to detect the microwave signal of the semiconductor, so as to obtain a time-resolved microwave photoconductive curve;

Carrying out frequency sweep of the whole frequency band on the microwave signal to obtain a time resolution microwave spectrum;

And acquiring semiconductor carrier dynamics information according to the time-resolved microwave spectrum.

2. The semiconductor carrier dynamics testing method according to claim 1, characterized in that: changing the light intensity and the irradiation wavelength of different bias background light to obtain a group of time-resolved microwave photoconductive curves, and fitting the time-resolved microwave frequency spectrums of the group of time-resolved microwave photoconductive curves to obtain carrier dynamics information.

3. The semiconductor carrier dynamics testing method according to claim 1, characterized in that: and changing the light intensity and the irradiation wavelength of different bias background light, obtaining time-resolved microwave photoconductive curves under different defect filling states, calculating the change of the Q value or the microwave reflectivity of the cavity according to the change of the amplitude and the frequency, and analyzing the microwave photoconductive characteristics of the semiconductor sample under steady state and excited state.

4. The semiconductor carrier dynamics testing method according to claim 1, characterized in that: the phase of the time-resolved microwave spectrum corresponds to the imaginary part of the dielectric constant of the semiconductor and is used for analyzing the dynamics of capturing deep energy level defects; the amplitude information of the time-resolved microwave spectrum corresponds to the real part of the dielectric constant of the semiconductor and is used for analyzing the light generation rate of carriers and dynamics caused by capturing shallow level defects.

5. The semiconductor carrier dynamics testing method according to claim 1, characterized in that: the analyzing semiconductor carrier dynamics according to time-resolved microwave spectrum includes: the energy level and density of semiconductor defects are analyzed by fitting different time-resolved microwave spectra.

6. The semiconductor carrier dynamics testing method according to claim 1, characterized in that: the method further comprises the steps of: detecting the attenuation of microwave signals under different time delays, and recording the dynamic process of carriers in the semiconductor sample.

7. The semiconductor carrier dynamics testing method according to claim 1, characterized in that: the method further comprises the steps of:

And comparing different time-resolved microwave spectrums, resolving the change of phase and amplitude information in a microwave signal, and distinguishing different types of carrier dynamics processes in a semiconductor.

8. A semiconductor carrier dynamics test apparatus, characterized in that: comprising the following steps:

An excitation light source for providing pulsed excitation light to the semiconductor sample to excite the semiconductor sample to generate photogenerated carriers;

A backlight source for providing bias backlight of different intensities to the semiconductor sample to fill different defect states of the semiconductor sample;

A microwave analyzer, which serves as a microwave source and detector, for acquiring a time-resolved microwave spectrum;

a spectrometer for recording a steady state photoluminescence spectrum;

a time-dependent single photon counter for acquiring a time-resolved photoluminescence spectrum;

The optical fiber coupler is used for coupling the pulse excitation light and the bias background light to one optical fiber; and

The light mixer is used for receiving the pulse excitation light and the bias background light transmitted by the optical fiber and uniformly mixing the pulse excitation light and the bias background light.