Abstract
Carbon doped GaN grown by hydride vapor phase epitaxy was investigated by photoluminescence and photoluminescence excitation spectroscopy covering a broad range of carbon concentrations. Above bandgap excitation reveals typical transitions related to CN and CN−Hi that decrease with increasing carbon concentration. Besides the formation of nonradiative defects, the formation of complexes containing more than one carbon atom is proposed to be responsible for this reduction. Below bandgap excitation reveals an intense emission band around 1.62 eV for [C] >1018cm−3 that is shown by photoluminescence excitation spectroscopy to be most efficiently excited at 2.7 eV. The 1.62 eV transition thermally quenches above 80 K. A configuration-coordinate diagram model is proposed to explain the observed emission, excitation, and thermal quenching behavior. Based on the simultaneous increase in the concentration of tri-carbon complexes, this band is tentatively attributed to a transition involving a deep tri-carbon-related charge state transition level in the GaN bandgap.
Highlights
INTRODUCTIONCarbon doping is widely used to implement highly resistive buffer layers in GaN based high power devices
Carbon doped GaN grown by hydride vapor phase epitaxy was investigated by photoluminescence and photoluminescence excitation spectroscopy covering a broad range of carbon concentrations
Bandgap excitation reveals an intense emission band around 1.62 eV for [C] .1018 cmÀ3 that is shown by photoluminescence excitation spectroscopy to be most efficiently excited at 2.7 eV
Summary
Carbon doping is widely used to implement highly resistive buffer layers in GaN based high power devices. Reshchikov et al have shown that CN is responsible for the yellow luminescence (YL) with a PL peak maximum around 2.2 eV3,12 and for a secondary PL band in the blue spectral region (BLC).. Besides carbon, hydrogen is present, both species tend to form CN–Hi complexes that are responsible for an intense blue luminescence (BL2) band with a peak maximum at Emax 1⁄4 3:0 eV and a zero. We present an investigation of the influence of carbon concentration on the PL emission of GaN using both above and below bandgap excitation. While for above bandgap excitation, the observed transitions are as expected for carbon doped GaN, our analysis of their evolution with carbon concentration contributes to the understanding of the formation behavior of the underlying, carbon-related defects. All spectra were corrected for the spectral response of the system
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