Abstract
We have measured photothermal spectra of bulk and film GaN crystals by the photothermal divergence (PTD) method in the temperature range from 110 K to 320 K. The band-gap energy of the GaN film grown by metalorganic chemical vapor deposition (MOCVD) method on a sapphire substrate shifts toward a higher energy because of the stress, compared with that of the bulk GaN grown by hydride vapor-phase epitaxy (HVPE) method. Moreover, the dependence of the PTD signal intensity, IPTD, on the doping has been observed. From IPTD spectra, we have found that a doping procedure may induce the degradation of the crystalline quality of GaN. For the bulk, two peaks in the energy region below the band edge have been observed in the IPTD spectra, and it has been found that such peaks may originate in nonradiative recombination centers. The two peaks have been characterized to be related to deep levels observed previously by means of the so-called deep-level transient-scan method.
Published Version
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