P. Dreszer

Electronic properties of low-temperature InP

We have investigated InP layers grown by low-temperature (LT) gas source molecular beam epitaxy. Using high-pressure hall effect measurements, we have found that the electronic transport in the LT epilayers is determined by the presence of the dominant deep donor level which is resonant with the conduction band (CB) located 120 meV above the CB minimum (ECB). We find that its pressure derivative is 105 meV/GPa. This large pressure derivative reveals the highly localized character of the donor which via auto-ionization gives rise to the high free electron concentration n. From the deep level transient spectroscopy and Hall effect measurements, we find two other deep levels in the band gap at ECB−0.23 eV and ECB−0.53 eV. We assign the two levels at ECB 0.12 eV and ECB−0.23 eV to the first and second ionization stages of the phosphorus antisite defect.

Optically detected magnetic resonance studies of low-temperature InP

We present experimental results from studies of low-temperature molecular beam epitaxially grown InP (LT InP), by optical detection of magnetic resonance (ODMR), where both the identification of defects and recombination processes can be studied simultaneously. The presence of the PIn antisites is unambiguously established, evident from the doublet hyperfine structure from the31P atom (with nuclear spin I=1/2 and 100% natural abundance). The PIn antisites are shown to be involved in strong nonradiative recombination processes, which compete with radiative ones via other defects. In addition to the PIn antisites, another defect has been detected in ODMR experiments which is shown to be a low-symmetry defect, likely a complex related to Be. Photo-excitation of the ODMR signals allows determination of the energy level positions of these defects. The results indicate that the PIn antisite is the prevailing defect governing the electronic properties of the material.

First direct observation of EL2-like defect levels in annealed LT-GaAs

Nonstoichiometric arsenic-rich GaAs grown at low temperatures by molecular beam epitaxy (LT-GaAs) has been found to be semi-insulating after high-temperature annealing. The origin of this technologically important conversion is not yet fully understood. In order to study this effect, we performed photocurrent measurements on p-LT GaAs-n diodes in the spectral range between 0.75 and 1.5eV at 8K. The photocurrent spectra revealed the following features which are unique to the EL2 level: photoquenching, characteristic photoionization transitions to conduction band minima and a presence of a broad band due to the effect of auto-ionization from the excited state. Moreover, modeling of the optical excitation process using realistic band structure demonstrates that these features cannot be explained by “internal photoemission” originating from As precipitates, as the “buried Schottky barrier model” predicts. This is the first direct experimental evidence for the existence of EL2-like defect levels and their importance for understanding the optical and electronic properties of annealed LT-GaAs.

Semi-insulating GaAs made by As implantation and thermal annealing

Abstract We have demonstrated that it is possible to regrow amorphous layers created by high dose As implantation in GaAs by thermal annealing in order to obtain arsenic precipitates distributed in a GaAs matrix similarly to that observed in low temperature GaAs. The characteristics of the As precipitates can be monitored through appropriate selection of the implantation and annealing conditions. Electrical measurements show that dielectric-like resistivity of surface or buried GaAs layers can be obtained by this method. Results on the growth of epilayers on these semi-insulating regions are also reported.