GaAs layers grown by molecular beam epitaxy (MBE) at substrate temperatures between 200 and 300 °C were studied using transmission electron microscopy (TEM), x‐ray diffraction, and electron paramagnetic resonance (EPR) techniques. High‐resolution TEM cross‐sectional images showed a high degree of crystalline perfection of these layers. For a layer grown at 200 °C and unannealed, x‐ray diffraction revealed a 0.1% increase in the lattice parameter in comparison with bulk GaAs. For the same layer, EPR detected arsenic antisite defects with a concentration as high as 5×10¹⁸ cm⁻³. This is the first observation of antisite defects in MBE‐grown GaAs. These results are related to off‐stoichiometric, strongly As‐rich growth, possible only at such low temperatures. These findings are of relevance to the specific electrical properties of low‐temperature MBE‐grown GaAs layers.

The concentration of the major electron trap (0.82 eV below the conduction band) in GaAs (Bridgman grown) was found to increase with increasing As pressure during growth. It was further found that (for a given As pressure) the concentration of this trap decreased with increasing concentration of shallow donor dopants (Si, Se, and Te). Donor concentrations above a threshold of about 10¹⁷ cm⁻³ led to the rapid elimination of the trap. On the basis of these findings, the 0.82‐eV trap was attributed to the antisite defect As_Ga formed during the postgrowth cooling of the crystals.

Intracenter transitions in the major deep level EL2 in GaAs were identified for the first time by superimposing photocurrent measurements on those of optical absorption. These transitions were found to be responsible for the characteristic EL2 absorption band between 1.0 and 1.3 eV. At low temperatures (<60 K) intracenter absorption exhibits a fine structure involving the zero phonon line and replicas at energies close to those of transverse acoustic phonons (TA). This coupling with TA phonons is a strong indication that EL2 is an extrinsic self-trapping center.

Microcrystalline Ga1−xMnxN samples with Mn content up to x=0.005 were grown by an ammonothermal method and were studied using various techniques. X-ray diffraction showed characteristic diffraction lines for hexagonal GaN phase mixed with a small contribution (<5%) from the Mn3N2 phase. Raman spectra exhibited characteristic peaks of pure GaN and modes that could be associated with Mn-induced lattice disorder. Electron spin resonance and magnetization measurements were consistent with the dominant Mn2+(d5) configuration of spin S=5/2 which is responsible for the observed paramagnetic behavior of the GaMnN material.

The magnetization of Ga1−xMnxN (x<0.1) crystals was measured as a function of the magnetic field and temperature. Paramagnetic behavior typical of spin S=5/2 expected for Mn2+ (d5) magnetic centers was observed in the temperature range of 2 K<T<300 K. On the other hand, antiferromagnetic coupling between Mn ions was clearly visible. The nearest neighbor (NN) coupling constant JNN/kB=−1.9 K was estimated from the temperature dependence of the magnetization.

We showed that hydrogen incorporated into single crystals of GaAs (by exposure of the crystals to hydrogen plasma) renders the major deep donor level (EL2) located at 0.82 eV below the conduction band at room temperature electronically inert. We attribute this passivation process to the interaction of hydrogen with the unsaturated bonds of the antisite As_Ga defect (believed to be responsible for EL2) leading to the formation of stable As–H bonds.