GaSb is a 111 ~ V group semiconductor material with narrow band gap, high carrier mobility and low effective carrier mass. It can be used to manufacture high-speed electronic devices, and can also be used for growth work at 0.8 ~ Base material for optoelectronic materials in the 4.3Mm wavelength range. Because of its good application prospects in low-loss optical fibers and high-efficiency solar cells, research on it has been strengthened in recent years 2'51. Intrinsic GaSb is always p-type conductive, and its hole concentration is about 1016 ~ 1017cm-3. It is reported that the residual acceptor is a double ionized background defect, and it is caused by the excess of Ga atoms 6 ~ 8. These residual acceptors are considered to be V (; aGaSb (GaSb is the inverse of Ga Defects) Defect complex 19101, but so far no direct evidence to prove this conclusion has been found.
In the past 20 years, positron annihilation technology has been widely used to study neutral and negatively charged vacancy defects in solids 1 "13. Neutral and negatively charged vacancies in solids will become traps for positron capture. Injection After being heated and diffused, the positrons will be preferentially captured by the neutral and negatively charged vacancies in the solid, and then annihilated, releasing two Y photons, and detecting the information brought by the Y photons can analyze the defects in the solid. Features. The positron annihilation rate is proportional to the electron concentration at the annihilation site, and annihilation at different types of vacancies has different positron lifetimes. Positron annihilation experimental data can not only give the relationship between lifetime and measured temperature, but also identify defects. Charge state and ionization energy.
Ling et al. 114161 reported that a lifetime component of approximately 315 ps was found in heavily doped Zn and undoped GaSb, and defects with a lifetime value of approximately 280 ps can be introduced into GaSb by electron irradiation. Through annealing and temperature experiments, they believed that the defects related to these two lifetimes were two types of gallium vacancy-related defects (VGa) with different microstructures. Dannefaei et al.17 reported that the GaSb sample of Te had a life component of 297ps and a body life component of 253ps. Puska et al. 118 reported that GaSb has a body life value of 260 ps, ​​Va life value of 287 ps, antimony vacancy-related defects (VSb) lifetime value of 307 ps, antimony vacancy and gallium vacancy composite defects (VSbVa) lifetime values ​​of 1017 cm-2 and 1.0 X 1018 cm2 ) Electron irradiation of GaSb materials, and the use of positron lifetime spectroscopy and Doppler experimental techniques to study the defects in the irradiated material, combining the positron lifetime at the defect and the electron momentum distribution to analyze the chemical environment around the defect.
1Experiment 1.1Experimental samples Experimental samples are made by refining single crystals by liquid-sealed Czochralski method, provided by Institute of Semiconductors, Chinese Academy of Sciences. The size is 10mmX10mmX0.6mm. One-sided chemical polishing. The characteristic parameters of the samples are shown in Table 1. The characteristic parameters of the samples used in the experiment Sample number Doping type Carrier concentration Irradiation dose Undoped Zn doped Te 1.2 Experimental method Electron irradiation Key experiment of radiation physics and technology in Sichuan University Room. The electron energy is 1.5MeV. The temperature of the sample is kept below 50C during irradiation. The samples are annealed isochronously at different temperatures (26 ~ 500, and positron lifetime spectrum measurement and Doppler broadening spectrum measurement are performed on these samples at room temperature .
The positron lifetime spectrometer uses the traditional fast time to meet the system. Each spectrum counts 2.5X16. Consistent with the Doppler broadening system includes two relatively placed high-purity germanium probes, each probe is about 20cm away from the sample. Each Doppler broadening spectrum counts 1.107. The peak-to-background ratio of the Doppler system is about 6.0X105. 2 Results and discussion The positron lifetime measurements of this experiment were all performed at room temperature, and the data were processed by the PATFIT program. For the original undoped sample, the two lifetime components can be used to solve the defect lifetime value (T) and the average lifetime value (T) of 283 ps and 265 ps. After electron irradiation, these values ​​become 284 ps and 268 ps. According to the positron Life formula: T = (E / i / T) -1 Calculate t in the material after irradiation is 258ps. T / Th = 1.10, indicating that the defects detected in the undoped GaSb sample after electron irradiation are Single vacancy defect. And this life value is consistent with the results reported by Puska et al. 1181 (see Table 2).
Table 2. Positron lifetime and intensity results of sample A. The radiation dose introduces vacancy-type defects with a lifetime value of 284 ps in the GaSb sample. This result is consistent with the results reported by Ma et al. 1191 (electron irradiation will introduce V in undoped GaSb samples; a, 28.ps defects). Electron irradiation produces an anomaly in sample C, that is, its average life decreases with the dose of electron irradiation. The same phenomenon also occurs in the proton irradiation experiment in this paper. This phenomenon needs further study.
Table 3 The positron lifetime results of the sample BCD. The dependence of the average positron lifetime of the undoped sample after the irradiation dose / cm electron irradiation on the annealing temperature and the annealing temperature can be seen. When the temperature is lower than 300C, the life spectrum is analyzed with a two-state capture model to obtain a better fitting result, and after the temperature is higher than 300C, the life spectrum is better fitted with a single life component, when the annealing temperature is lower than 300 ° C The average life time decreases with the increase of annealing temperature. After 300 ° C, the average life time of the positron almost no longer changes. This shows that the defects in the sample can be annealed at 300C. In this work, the annealing behavior of the sample after electron irradiation is consistent with the previous work result 120 in this laboratory.
The lifetime value is close to 284 cells. Therefore, the author believes that electron f irradiation will show from Table 2 that the defect life of undoped samples before and after irradiation does not change significantly, and the reason for the large average life is that the defect component is large (from 84% becomes 87%), that is, the concentration of defects is large, indicating that electron irradiation introduces the same defects in the sample as the original sample, so that the defect concentration in the sample is large and the average life is large. Table 3 lists sample B respectively , C, D average life and defect life values ​​after different doses of electron irradiation. From the table, it can be found that the defect life values ​​measured by these samples after electron irradiation are Doppler broadened spectrum 2 ° ~ 221 It is used to identify the chemical environment of defects in different materials and the sublattice of defects. The high momentum region in the Doppler broadened spectrum reflects the annihilation of core electrons, the distribution of electron shells around different atoms is different, and the positrons are around different atoms The characteristics of drowning are also different. In order to distinguish this information more clearly, a Doppler broadened spectrum of a standard sample is often selected as the data during data processing, and divided by other Doppler broadened spectra. From this spectrum, a quotient spectrum (normalized spectrum) is obtained, and the formula is expressed as R (E) / N0 (E). By analyzing the quotient data, the element X around the defect can be obtained to represent the original sample A. Electron irradiation (10l7cm-2 ) Sample A and electron-irradiated sample tlecfronicPublishiSg element and clock element after annealing at low f temperature; adjacent 1 may be shown in ink 1 in v.
Ma et al. 119 reported that electron irradiation of GaSb will introduce defects Vr; a, 28 ps. This lifetime value is very close to the lifetime value of 287 ps reported by Puska et al. 1181, and the original and irradiated ones found in this work The lifetime values ​​of defects in GaSb samples are 283 ps and 284 ps, respectively. These two lifetime values ​​are very close to the above-mentioned reports. Such defects will be rejected at 300C. At the same time, in the electron-irradiated samples B, C, and D, the normalized Doppler spectrum of the defect showed a negative slope characteristic in the momentum range of 1.10-2m0c, which shows that these samples were introduced after electron irradiation A large number of related defects VGa, see the results.
It can be seen that Sample B shows the characteristics of Ga element (positive slope) before irradiation, but it shows the characteristics of Sb element (negative slope) after electron irradiation. The Doppler broadening spectra of the two samples C and D almost coincided with the line of the sample A after irradiation, and the sample C after electron irradiation also showed a negative slope, which shows that these The defects in the sample were consistent with the defects in the undoped sample after irradiation. Although the slope characteristic in the periodic table of the 3 conclusions is the characteristic of the Te element, the Zn element is adjacent to the Ga element in the periodic table, and the negative slope shown shows that the defect in the Zn-doped sample after electron irradiation must be around It is the Sb atom, which also indicates that the defect must be the related defect Va. Before irradiation, the sample Zn contains the impurity ZnVa complex. Because the stable Vsb defect is positively charged, it cannot capture positrons.
Samples B, C, and D are all doped materials. In these samples, there are defects that lack the vacancy complex type. It can be seen from Table 3 that after high-dose (10X18cm-2) electron irradiation, the positron lifetimes in these samples tend to be consistent (285 ± 5, 284 ± 4, 284 ± 6ps), so the author believes that electron irradiation The defects of the vacancy complex type in these materials have a very large impact. Ling et al. 1141 reported that there is a defect in the Zn-doped GaSb sample, and Puska et al. 118 calculated this lifetime value as 287ps. Ling et al. Explained that the theoretical calculation may not consider the factors around the defect to relax around. . The author believes that Ling probably did not consider the existence of ZnVa-type defects in the Zn-doped samples, and the value reported by them is probably the life value of this type of defect. In Table 3 of this article, the defect life value of sample B when not irradiated is 295 ps, and the life value after irradiation becomes a basis for the author's conclusion from another aspect. Therefore, the author believes that electron irradiation affects ZnVa-type defects, so that the Zn atoms at this defect will either enter the vacancy to make this defect disappear, or diffuse from the defect into the material, making this defect a pure Voa Vacancy defects. In sample C, the Doppler curve after electron irradiation showed a significant negative slope, while the slope of the Doppler curve before irradiation was almost zero. Combining life spectrum experiments (only single-defect model fitting before and after irradiation) shows that electron irradiation also has an effect on defects in Te-doped samples. The defect in the original sample becomes a Voa-related defect (the negative slope of the Doppler curve is characteristic of Sb atoms) or disappears.
To sum up, electron irradiation introduces defect VGa 284ps in sample A. This kind of defect with lifetime value has almost the same lifetime value as the defect Va283ps in the sample before irradiation, so I think this is the same kind of defect, Electron irradiation simply increases the concentration of such defects in the sample. Electron irradiation has no effect on the defect GaSb. In Zn-doped samples, electron irradiation will affect ZnVGa-type defects, either make this type of defects disappear, or make this type of defects become pure VGa vacancy-type defects. The same phenomenon also exists in the Te-doped samples (the phenomenon is more doped in the GaSb samples in the heavily doped Te samples. Both life components can be used to fit the life spectrum before and after irradiation well, and the life values ​​are consistent. Irradiation introduces Va-related defects with a lifetime value of 284ps in the native GaSb. This defect has the same lifetime value as the defect in the original non-irradiated sample (VGa283ps), but the concentration of this defect is after electron irradiation. Significantly large. It shows that the defects introduced by electron irradiation are consistent with the microstructure of the original unirradiated sample, and the defects are introduced by electron irradiation. Such VGa-related defects will retreat at 300 C.
The low-temperature Doppler broadening spectrum after annealing shows that the GaSb samples still have the anti-site defect GaSb mentioned by Hu et al. 120. The Doppler experiments of the Te-doped and Zn-doped samples also confirmed that the electron irradiation would Introduce Voa related defects. And electron irradiation has an effect on the original defects in these samples, so that these defects disappear or become pure VGa vacancy type defects.
Guangdong Decosun Lighting Technology Co.,Ltd , https://www.decosun-lighting.com