CN204905216U - Measure device of amorphous silicon thin film band gap defect density of states - Google Patents

Abstract

The utility model provides a measure device of amorphous silicon thin film band gap defect density of states, includes: the exciting light source, what it sent shines solely, dielectric material, need checking sample dipes dielectric material, it arrives to shine the light struck thereby dielectric material arouses that dielectric material's refracting index changes around the need checking sample, causes to arouse from this the refracting index changes in need checking sample's the skin layer, laser probe, its light signal that sends passes dielectric material, and because of dielectric material's refracting index changes and takes place to deflect, position sensor, its sensing deflect and send the deflection signal, and accounting device, its basis the signal that deflects calculates the thin film materials's that surveys the defect density of states. According to the utility model discloses a measure device of amorphous silicon thin film band gap defect density of states measures thin film materials's light absorption and sets to music the defect attitude of testing in the material, to low energy end (< 1.1eV) the absorption higher sensitivity has to the defect attitude that can comparatively accurately measure the material distributes.

Description

Device for Measuring Bandgap Defect State Density of Amorphous Silicon Thin Film

technical field

The utility model relates to a device for measuring the band gap defect state density of an amorphous silicon thin film, which belongs to the technical field of semiconductor thin films, in particular to a silicon-based thin film defect state density testing device for thin film solar cells.

Background technique

Thin-film solar cells with hydrogenated amorphous silicon (a-Si:H) thin film as the absorbing layer have high light sensitivity (about 105 orders of magnitude) due to the large light absorption coefficient of amorphous silicon material, and its absorption peak is similar to that of The solar spectrum is close, which is conducive to the full use of sunlight. Because it also has the advantages of easy large-scale, continuous, and automated production, it occupies the leading position in the second generation of solar cells, that is, thin-film solar cells.

Hydrogenated amorphous silicon (a-Si:H) itself has the problem of poor stability. In 1977, Stabler and Wronski discovered that hydrogenated amorphous silicon, especially intrinsically hydrogenated amorphous silicon (type I undoped), was After light irradiation, its photoconductivity and dark conductivity decrease significantly, but under the condition of above 150℃ without light annealing, hydrogenated amorphous silicon can return to the state before light irradiation, which is the photodegradation effect of hydrogenated amorphous silicon (S-W effect). Due to the existence of light-induced degradation effect, the photoelectric characteristics of hydrogenated amorphous silicon will deteriorate after long-term use, and even fail, resulting in the performance of amorphous silicon thin-film solar cells using it as the absorbing layer seriously declines with the light, so the light stability It has become one of the biggest bottlenecks restricting the development of amorphous silicon thin film solar cells. A large number of experimental and theoretical works have focused on the research on the characteristics and origin of the light-induced degradation effect. The general view is that the S-W effect is caused by light, which leads to the generation of new dangling bond defect states (deep energy levels) in the band gap. This defect state will affect the position of the Fermi level EF of the hydrogenated amorphous silicon (a-Si:H) film material, so that the distribution of electrons will change, which will cause changes in optical properties on the one hand, and on the other hand. effect on the compounding process. These defect states become additional recombination centers for electrons and holes, which increases the capture cross section of electrons and decreases their lifetime.

Utility model content

The utility model aims to provide a method for testing the defect state density of a silicon-based thin film, and further provide a solution for improving the material properties of a silicon-based thin solar cell.

In order to achieve the above object, a device for measuring the density of states of defects in the bandgap of an amorphous silicon thin film is provided, including: an excitation light source, which emits irradiation light; a dielectric material, into which the sample to be measured is immersed, and the irradiation light To the dielectric material, the refractive index of the surrounding dielectric material of the sample to be tested changes, thereby causing the refractive index in the thin surface layer of the sample to be tested to change; the laser probe, the optical signal emitted by it passes through the The dielectric material is deflected due to the change in the refractive index of the dielectric material; a position sensor senses the deflection and sends a deflection signal; and a computing device calculates the defect of the measured film material according to the deflection signal density of states.

In some embodiments, the excitation light source is a monochromator.

In some embodiments, the dielectric material is carbon tetrachloride.

According to the device for measuring the bandgap defect state density of amorphous silicon thin film of the present invention, the defect state in the material is tested by measuring the optical absorption spectrum of the thin film material, and has higher sensitivity to the absorption at the low energy end (<1.1eV), and The defect state distribution of materials can be measured more accurately.

In the following, the gist of the utility model is illustrated by examples in conjunction with the accompanying drawings, so as to clarify other aspects and advantages of the utility model.

Description of drawings

The above-mentioned and other features and advantages of the present utility model can be more clearly understood through the following detailed description in conjunction with the accompanying drawings, wherein:

1 is a schematic diagram of a device for measuring the density of states of defects in the bandgap of an amorphous silicon thin film according to an embodiment of the present invention; and

Fig. 2 is a defect state density map of an amorphous silicon thin film tested by the device of the present invention.

Detailed ways

Referring to the accompanying drawings of specific embodiments of the utility model, the utility model will be described in more detail below. However, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are presented so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

The device for measuring the bandgap defect state density of an amorphous silicon thin film according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

The device for measuring the bandgap defect density of states of an amorphous silicon thin film according to an embodiment of the present invention includes: an excitation light source, which emits irradiation light; a dielectric material, into which the sample to be tested is immersed, and the irradiation light irradiates the The dielectric material causes the refractive index of the dielectric material around the sample to be tested to change, thereby causing the refractive index in the thin surface layer of the sample to be measured to change; the laser probe, the optical signal it sends through the medium material, which is deflected due to the change in the refractive index of the medium material; a position sensor, which senses the deflection and sends a deflection signal; and a computing device, which calculates the defect state density of the measured thin film material according to the deflection signal .

A device for measuring the density of states of defects in the bandgap of an amorphous silicon thin film, as shown in Figure 1, comprising a monochromator 1, a chopper 2, a photoelectric receiver 3, a laser probe 4, a dielectric material 5, and a sample to be tested 6 , a position sensor 7, a preamplifier 8, a dual-phase lock-in amplifier 9, a lock-in amplifier 10, and a computer data system 11.

The chopper 2 modulates the continuous light into light with a fixed frequency. The photoelectric receiver 3 converts the monochromatic light signal sent by the monochromator into an electrical signal. The preamplifier 8 is used to amplify the output signal of the sensor, and the dual-phase lock-in amplifier 9 and the lock-in amplifier 10 are used to track the optical signal of a fixed frequency for comparative detection. The computer data system 11 is mainly used to control the monochromator and deliver monochromatic light according to the change of the step size, as well as subsequent data processing.

When the dielectric material 5 is irradiated by the exciting light emitted by the monochromator 1, the absorbed energy will be periodically converted into heat energy, and the heat flow will flow out from the heated area to the surroundings, causing the temperature of the dielectric material 5 itself and its surroundings to rise, thereby causing Changes in the refractive index within a thin layer on the surface of sample 6. The optical signal emitted by the laser probe 4 will be synchronously deflected due to the change of the refractive index of the dielectric material 5, and the periodic deflection is detected by the position sensor 7, and the output signal S of the sensor can be amplified by the position sensor and a lock-in amplifier for observation. S is determined by the following formula:

S＝C[1-exp(-α×d)]×(1-R _F )×(1+R _B )/(1-R _F R _B )

In the formula, R _F and R _B are the reflection coefficients of the front and rear surfaces of the film respectively; α is the absorption coefficient of the material; d is the thickness of the film. Usually _RB can be ignored. In the high photon energy region (αd>>1), the signal tends to be saturated.

S/S _saturation =1-exp(-α×d). Therefore, as long as the thickness of the sample is known, the absorption coefficient α can be obtained from the above formula. Compared with single crystal silicon, the absorption of thin film silicon material at the low energy end (<1.1eV) is significantly increased, which is mainly related to the defects of the material.

Example

Figure 2 is a diagram of the defect density of states of an amorphous silicon film tested by the device of the utility model, and the defect density of the silicon film obtained by the above formula is 2.3E15cm ^-2 .

According to the device for measuring the bandgap defect state density of amorphous silicon thin film of the present invention, the defect state in the material is tested by measuring the optical absorption spectrum of the thin film material, and has higher sensitivity to the absorption at the low energy end (<1.1eV), and The defect state distribution of materials can be measured more accurately.

The preferred specific embodiments of the present utility model have been described in detail above. It should be understood that those skilled in the art can make many modifications and changes according to the concept of the present utility model without creative efforts. All technical solutions that can be obtained by those skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present utility model on the basis of the prior art shall be within the scope of protection defined by the claims.

Claims (3)

1. A device for measuring the density of states of an amorphous silicon thin film bandgap defect, characterized in that it comprises: Exciting light source, which emits illuminating light; The dielectric material, the sample to be tested is immersed in the dielectric material, and the irradiating light is irradiated on the dielectric material to cause the refractive index of the dielectric material around the sample to be tested to change, thus causing the inner layer of the surface thin layer of the sample to be tested to The refractive index changes; a laser probe that emits an optical signal that passes through the dielectric material and is deflected by a change in the refractive index of the dielectric material; a position sensor that senses the deflection and issues a deflection signal; and A calculation device, which calculates the defect state density of the measured thin film material according to the deflection signal. 2 . The device for measuring the bandgap defect density of states of an amorphous silicon thin film according to claim 1 , wherein the excitation light source is a monochromator. 3 . 3 . The device for measuring the bandgap defect density of amorphous silicon thin films according to claim 2 , wherein the dielectric material is carbon tetrachloride. 4 .