A deep level transient spectroscopy analysis of electron and hole traps in bulk-grown GaAs

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Abstract
The electron and hole traps occurring in melt-grown undoped n-type GaAs have been studied using deep level transient spectroscopy. Several electron traps with energies ranging from 0.81 to 0.14 eV below the conduction band, as well as three hole traps having energies 0.65, 0.56, and 0.43 eV above the valence band, were measured. Isochronal annealing in the temperature range 500–800 °C indicated that, under optimized ‘‘face-to-face’’ annealing conditions, an 800 °C heat treatment for 1 h resulted in the removal of all the electron traps, with the exception of the EL2 (0.81 eV). Near the surface, however, this annealing procedure reduced the EL2 concentration by more than an order of magnitude. It was further observed that, when a sample is annealed ‘‘face-to-face’’ with another sample, the total defect concentration is reduced much more than when a sample is covered with graphite as during a standard liquid-phase epitaxy (LPE) pregrowth anneal cycle at the same temperature. The effect of surface damage during mechanochemical polishing on defect concentration has also been demonstrated.