LEC-grown Semi-insulating GaAs Research Articles

Direct Evidence for a Charge-Controlled Optical Quenching of EL2 Centers in Semi-Insulating GaAs

We present results of microwave photoconductivity as well as far-infrared laser magnetooptical absorption measurements obtained for LEC (liquid encapsulated Czochralski)-grown semi-insulating GaAs crystals. At low temperature we have observed a “photo-quenching effect” both for signals of microwave photoconductivity and for the shallow donor Zeeman absorption measured using a far-infrared laser, under the condition of BBG (below-band-gap) photoexcitation. Through these experimental observations, we conclude that the shallow donor is associated with the metastable state of the EL2 center in LEC-grown semi-insulating GaAs. From the temperature dependence of microwave photoconductivity decay with BBG pulsed photoexcitation, we can estimate the characteristic activation energy, ΔEA=240 meV, which originates from a barrier in the conduction band related to the Franck-Condon shift of the EL2 metastable state.

Investigation of negative transient current of argon-implanted GaAs using photoinduced transient-current spectroscopy

The investigation of deep levels of argon-implanted LEC-grown semi-insulating GaAs with implantation dosages ranging from 1*1011 to 1*1015 cm-2 has been performed. Using a photoinduced transient-current spectroscopy (PITCS) it was demonstrated that, for implantation dosages below 1*1013 cm-2, a negative peak or negative transient current (NTC) was observed in the temperature range from 330 to 350 K. The magnitude of this negative peak increased with dosage up to a level of 1*1012 cm-2, beyond which it decreased with dosage. The dosage dependence of the EL3 peak height and the resistance of the specimen have also been investigated. It was observed that the variation of the EL3 peak height with dosage was similar to the variation of the magnitude of the negative peak, that is the EL3 peak height likewise increased with dosage up to 1*1012 cm-2, and then decreased. The resistance of the original high-resistivity specimen dropped abruptly when the dosage reached 1*1012 cm-2. This critical dosage (1*1012 cm-2) was found to be a threshold for the generation of a highly disordered state.

Study of strain variation in LEC-grown GaAs bulk crystals by synchrotron radiation X-ray topography

Lattice distortions in LEC-grown semi-insulating GaAs bulk crystals are studied mainly by synchroton X-ray topography. Besides the microscopic lattice orientation and lattice parameter variations relating to the dislocation generation by thermal stress after growth, microscopic variation of the lattice parameter in a single cell is observed, which may be intrinsic due to some interaction of excess arsenic atoms with the entangled dislocations forming the cell walls.

Photoluminescence decay mechanism of the ≈1.49 eV emission in LEC-grown semi-insulating GaAs

A mechanism is proposed to explain the temperature dependence of the exponent of the power law: p( T) = -1 + βT of the ≈1.49 eV emission in semi-insulating GaAs.

Acoustic paramagnetic resonance of vanadium in semi-insulating GaAs

The authors report strong acoustic paramagnetic resonances (APR) from LEC-grown semi-insulating GaAs:V. The results obtained are consistent with observations made on similar samples by other workers using thermally detected electron paramagnetic resonance (TDEPR). The results can be interpreted as being due to a V2+-X centre producing phonon scattering where X is some other lattice defect or impurity associated with the vanadium. In one sample the APR is only observed after illumination of the sample while another sample that contained fewer impurities apart from vanadium showed the APR in the dark and enhancement after illumination. They suggest that illumination converts V3+-X centres into V2+-X by capturing an excited electron in the former case whereas in the second case illumination converts V+-X centres into V2+-X centres and the electron released is trapped at another site with a very long life at low temperature.

Analysis and Comparison of EL2 Concentration and Stress Distribution in Undoped LEC-Grown Semi-Insulating GaAs Ingots

AbstractNear-IR absorption mapping has been used for polished GaAs wafers (0.5 mm thick) cut at intervals along the seed-to-tail length of (100)-oriented LEC-grown semi-insulating (SI) ingots. Some 2000 points are measured, point by point, over a wafer's area, usually near 1.0 μm for EL2 mapping, and near 1.4 μm for observation of stress interferograms. For the results presented here (high pressure LEC crystals from a major commercial supplier), stress maps display the fourfold symmetry predicted in thermoelastic models. The EL2 maps do not necessarily display the same symmetry, especially for wafers from near the tail end of an ingot.

Dislocations as the origin of threshold voltage scatterings for GaAs MESFET on LEC-grown semi-insulating GaAs substrate

This paper describes the extended results on the influence of dislocations in liquid-encapsulated Czochralski (LEC) grown semi-insulating GaAs substrates on threshold voltage of GaAs MESFET's. MESFET's located less than about 50 µm from a dislocation exhibit threshold voltage lower than those far from a dislocation and threshold voltage scatters at less than about 30 µm from a dislocation. The scattering is considered briefly from anisotropy of stress field around dislocations. Particular interest is devoted to the electrical properties around dislocations because of their detrimental influence on the FET threshold voltage.

Lattice Bending in LEC-Grown Semi-Insulating GaAs Wafers

Lattice bending in LEC-grown semi-insulating GaAs crystal wafers was investigated by X-ray diffraction. Various distributions in the lattice bending were observed in wafers from different boules. Prominent bends, with radii of curvature of about 20 m, were observed at places where the relevant topographs showed the presence of fine cellular dislocation networks. The apparent wafer bending was also examined optically and was found to be caused mainly by back surface damage.