A low-cost microprocessor-based Deep-Level Transient Spectroscopy (DLTS) system

A microcomputer-based DLTS system is presented, in which the microcomputer functions as a signal averager and controller. The system can detect traps deeper than 0.20 eV from the band edges and 10³ cm^-3 less dense than the intentional dopant concentration. The system was applied to the study of deep traps in liquid-phase epitaxy (LPE) grown GaAs and vapor-phase epitaxy (VPE) grown GaAs_0.75P_0.25 light-emitting diodes (LEDs). A deep donor level at E_c -0.70 eV and σ_n=1.3×10^-15 cm² was found in the latter which agreed with capacitance-transients experiments done by another investigator. The electric-field strength was seen to inversely affect the electron capture cross section of this level. A minority-carrier trap reported at E_v+0.15 eV was observed but its energy level was not resolved due to its broad DLTS spectrum peak. The GaAs LED exhibited emission from a deep acceptor level at E_ν+0.81 eV and σ_p=2.2×10^-15 cm², σ_n=6.8×10^-22, and a deep donor level which could not be resolved.