Capacitance spectroscopy of heteroepitaxial AlGaAs/GaAs $p$–$i$–$n$ structures

Temperature dependences of capacitance-voltage ($C$–$V$) characteristics and deep-level spectra of the graded highvoltage AAl$_{x}$Ga$_{1-x}$As $p^{0}$–$i$–$n^{0}$ junction grown by liquid-phase epitaxy via autodoping with background impurities were investigated. The changes of the $C$–$V$ characteristics at varied measurement temperature and optical illumination demonstrated that the $p^{0}$-, $i$-, $n^{0}$-type layers in the Al$_{x}$Ga$_{1-x}$As under study contain bistable DX centers. In spectra of deep-level transient spectroscopy (DLTS), measured at various bias voltages $V_r$ and filling pulses $V_f$ , a positive DLTS peak is observed for the $n^0$-type layer with thermal activation energy $E_t$ = 280 meV and electron-capture cross-section $\sigma_n$ = 3.17 $\times$ 10$^{-14}$cm$^2$, which is unusual for a majority-carrier trap. This peak is related to the negatively charged state of the Se/Te donor impurity, which is a bistable DX center with negative correlation energy $U$.