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Home > News > Pulsed photo-ionization spectroscopy in carbon doped MOCVD GaN epi-layers on Si
Pulsed photo-ionization spectroscopy in carbon doped MOCVD GaN epi-layers on Si

GaN with intentionally incorporated carbon to create semi-insulating buffer layers shows improved performance in AlGaN/GaN heterojunction field effect transistors. Moreover, various impurities and crystal imperfections of GaN epi-layers determine a rather rich spectrum of deep levels. Thus, spectroscopy of defects is of paramount importance in optimizing GaN-based devices. In this work, pulsed photo-ionization spectroscopy (PPIS) has been applied to trace the prevailing defects and simultaneously monitor variations of carrier lifetime in metal−organic chemical vapor deposition grown GaN epi-layers on Si substrates of various carbon content concentration. A contactless technique for microwave probed photoconductivity has been employed to measure changes in excess carrier density, in order to evaluate variations in carrier lifetime and reveal the type of photo-activation processes. Six PPI spectral steps have been resolved in samples containing either superlattices (SLs) or AlN/AlGaN stress management layers. Three of these centres, namely,  and (CNON)0, have been associated with carbon dopants. Other PPIS peaks have been ascribed to Ga vacancies and metal impurities. It has been deduced from analysis of the PPIS peak broadening factor that rather strong electron−phonon coupling is inherent in photo-ionization of carbon related complexes at room temperature. The concentration of separated defects and cross-sections for photon−electron coupling have been determined using calibration measurements of optical transmittance spectra and correlations between microwave probed photoconductivity peak signals and absorption coefficient.

 

Source: iopscience

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