Improvement in semi-insulating GaAs material quality: A comparative study of defects with deep levels

Thermally stimulated currents (TSC) spectra and photocurrent (I-PC) measurements were used for detection and evaluation of defects with deep levels in undoped semi-insulating (SI) GaAs crystals. Large number of liquid encapsulated Czochralski (LEC) grown materials, produced from late 80's till nowadays, provided from ten various sources were analysed. Deep levels were characterised by a new analytical method-simultaneous multiple peak analysis (SIMPA) of TSC spectra. For each deep trap its unique and reliable signature was determined, comprising activation energy, E-a, electron capture cross section, sigma(n), as well as peak maxima, T-m, and trap's relative and absolute concentrations. It has been found that all measured TSC spectra, even having dramatically different shapes, can be excellently described with a limited set of 11 deep traps. Considerable improvement in quality of the SI GaAs materials produced during last decade was found. It reflects in concentration reduction of most defects and much better defect's distributional uniformity along the same as well as among different wafers, and in similarity of I-PC transients.