Photoluminescence and photoreflectance measurements are carried out in order to investigate the effects of annealing and hydrogenation on the defect levels of neutron‐transmutation‐doped (NTD) GaAs. The damage to the crystallinity of NTD GaAs is recovered by annealing, and the defects in the annealed NTD GaAs are compensated for by hydrogen atoms after hydrogenation. Since the transmutation‐doped impurities in GaAs are compensated for by the injection of hydrogen atoms, Franz‐Keldysh oscillations appear due to the large variation in the surface electric field.

Photoluminescence measurements are carried out in order to investigate the effects on the defect levels of neutron‐transmutation‐doped (NTD) GaAs due to annealing and hydrogenation. The peak intensity corresponding to the transition from the conduction band to the Ge acceptor [Ge(B–A)] increases at an annealing temperature of 600°C, and then decreases remarkably around a temperature of 650°C; on the other hand, the peak intensity of the defect complex peak increases at 600°C. After annealing and subsequent hydrogenation, the peak of the transitions between the band and the carbon acceptors [C(B–;A)] is resolved clearly into the C(B–A) and Ge(B–A) peaks, and the intensity of the peak corresponding to the As vacancy and carbon complex center on As sites decreases remarkably. These results indicate that the crystallinity of the NTD GaAs is improved by annealing and hydrogenation and that the defect complex center is passivated by thermal treatment and hydrogenation.

Photoluminescence (PL) spectra as a function of rapid thermal annealing (RTA) temperature are measured for semi‐insulating undoped GaAs irradiated with low‐ and middle‐level neutrons and also after hydrogenation. In the case of the irradiation with low‐level neutrons, C(B–A) and Ge(B–A) peaks at 800°C increase remarkably, and C(D–A) and Ge(D–A) peaks appear weakly together with C(B–A) and Ge(B–A). The intensity of Ge(B–A) transitions is almost comparable to that of C(B–A) transitions as the carbon concentrations in GaAs wafers (usually ≈ 1015 cm−3) are competitive with the transmuted Ge concentrations estimated from doping (≈ 1015 cm−3). After hydrogenation, Ge(B–A) peaks decrease and C(D–A), Ge(D–A) peaks disappear due to the passivation by hydrogen. In the case of irradiation with middle‐level neutrons the Ge(B–A) peaks including Ge(D–A) increase significantly, and C(B–A) peaks are concealed by Ge(B–A) peaks because the Ge concentrations (≈ 1016 cm−3) transmuted by the irradiation of middle‐level neutrons exceed the carbon concentrations in the GaAs wafer. After exposure of the same samples to a hydrogen plasma, Ge(B–A) peaks decrease apparently due to passivation. When furnace annealing was carried out for the same sample irradiated with middle‐level neutrons, the VAs–CAs defect complex center is observed around 879 nm because of the influence of the carbon susceptors. In the present study, the VAs–CAs defect complex is not observed after RTA. Therefore, it is confirmed that the VAs–CAs defect complex appearing after furnace annealing is correlated with carbon in the sample holder during the thermal treatment.

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