Fine Structures Of Energy Levels Of DX Centers In AlGaAs:Sn Alloy Semiconductors

Impurities and defects is an important subject in the semiconductor research work. DX centers, one of deep centers related to donors, have been found to be the universal deep states in most of III-V alloy semiconductors. They are characterized by several unusual properties, such as a large difference between thermal and optical ionization energies and extremely small electron capture cross sections that at low temperatures give rise to persistent photoconductivity (PPC), which attracted people's great interests. Until now, in spite of many investigations about DX centers' physical origins and energy levels' fine structures, there are still many problems that have not yet been classified. Therefore, with the wide applications of III-V alloy semiconductors in various types of novel electrical and optical devices, analyzing fine structures of DX centers in III-V alloy semiconductors in detail has great value of applications and academic significance.In this paper, voltage transients due to thermal electron capture and emission of DX centers in n-type Sn-doped AUGai.jAs (x = 0.26) were measured by the constant capacitance voltage transient (CCVT) technique. We found that capture transients shortened while raising the temperature. Analyzing their respective half logarithms curve of transient spectroscopy, we found all of them are non-exponential processes. Laplace defect specrroscopic (LDS) spectra of capture process were obtained by undertaking numerical Laplace transformation of CCVT signals in different temperatures. Every LDS spectrum has several discrete peaks. By decreasing temperatures, the peaks shifted to left and their number increased.The LDS spectra of thermal emission processes were also obtained with different capture times under several temperatures. The number of spectra peaks increased as lengthening capture period. Moreover, the increased spectra peaks emerged in left of the abscissa, that is, in the side of low emission rate. So the corresponding relation between the LDS spectra of emission and capture process was determined.The values of capture barriers determined by linear fitting of the slope of the Arrhenius plot of thermal capture coefficients were 0.232, 0.229, 0.226, 0.169 and 0.167 eV, respectively. Their binding energies were obtained by subtracting the capture barriers from relevant activation energies. Moreover, we also deduced their correspondent values of lattice relaxation energy and optical ionization energy.The results of our experiment show that the fine structures of energy levels of DX centers in AlojgGaa/^As: Sn could be classified into two groups, DX' and DX~ centers, respectively. The differences between the two groups could be indicated they were from different physical origins. We adopted the pseudopotential method and the first principle to calculate the alloy disorder effect of the atoms surrounding the impurity atoms. The results show that fine structures of the two DX-like centers are mainly contributed to second nearest Al/Ga atoms at different local configuration of Sn donor impurities due to the alloy random effect. Specifically, the relaxation of Sn and As atoms result in the fine structures of DX~ and DX' centers respectively.