Photoinduced transient spectroscopy and photoluminescence studies of copper contaminated liquid-encapsulated Czochralski-grown semi-insulating GaAs

Abstract

Photoinduced transient spectroscopy (PITS) studies of samples of copper contaminated annealed semi-insulating GaAs in the temperature range of 274–384 K show two dominant levels at about Ev +0.5 eV and about Ec −0.59 eV in addition to the EL2 levels at about Ec −0.80 eV. Depth profiling using chemical etching followed by PITS measurements shows a competing process between the defects responsible for the level at Ev +0.5 eV and that at Ec −0.59 eV. The former is predominantly found near the surface and the latter is dominant in the interior. From the depth profiling results, we have determined that the diffusion constants for these two types of defects are about 4.7×10−10 cm2 s−1 and 5.2×10−10 cm2 s−1, respectively. We propose that the level at Ev +0.50 eV is due to a copper related complex and the level at Ec −0.59 eV is due to native defects. The copper related level at about Ev +0.50 eV is different from the often seen copper related defect level at around Ev +0.40 eV. The presence of these two levels would explain the variety of results reported by different workers on the deep levels attributed to copper. Photoluminescence measurements on a copper contaminated sample at 4.2 K show a peak at 1.36 eV which is due to CuGa acceptor level. This peak appears even after repeated etching of the sample, showing the presence of copper throughout the sample. Comparison data were also obtained for both ‘‘copper-free’’ annealed and unannealed samples.

Vacancy generation during Cu diffusion in GaAs

“…8͒. 20,21 In contrast, in SI GaAs annealed at P As = 0.2 bar, no sign of Cu in the neighborhood of detected vacancies was observed.…”

“…18 The two-component trapping model and the specific trapping coefficient of 10 15 s −1 at 300 K were used for calculating the vacancy concentrations. Since Cu is the most common impurity in annealing studies, 6,20,21 Cu is the first candidate that can be responsible for the formation of such complex. 7͒ represent the power law and yield an exponent close to 0.25 for GaAs:Si and −0.25 for SI GaAs.…”

Optical properties and annealing effects on the deep levels in As-doped CdTe/Cd0.96Zn0.04Te (211) B heterostructures

“…Using Eq. 18,19 The H 4 peak occurring at 200 K is considered to be due to native defects or Te precipitates, and the H 5 peak is due to a defect level related to Cd vacancies. 3, is 7 meV.…”

EL2 and gallium antisite defects in GaAs: Si

“…The decrease in the concentration of both centers after annealing could be due to an amihilation process given by As,, + Ga,, As,, + G k , In the case of the 1.325 eV peak, PL studies of annealed samples show a reduction in the total intensity despite the presence of the LO phonon peak of Cu,, at 1.324 eV (16). Copper contamination is inevitable during annealing in a quartz ampoule (13,17). This reduction follows the behavior of the peak at 1.443 eV, which is another indication that they are related.…”

“…The excitation source was a nitrogen laser-pumped dye laser at 620 nm wavelength. Data acquisition was done automatically using the photoluminescence spectroscopy system described by Tin et a1 (13). The PL spectra for the samples at 4.2 K are shown in Fig.…”