A study of subbands in AlGaN/GaN high-electron-mobility transistor structures using low-temperature photoluminescence spectroscopy

Abstract

Al 0.15 Ga 0.85 N/GaN high-electron-mobility transistor (HEMT) structures with various δ-doping concentrations and spacer thicknesses grown on sapphire by metalorganic chemical-vapor deposition are investigated. The Hall mobility is as high as 1333 cm2/V s at room temperature and 6330 cm2/V s at 77 K. Two-dimensional electron gas (2DEG) phenomena, which have not been clearly resolved in the literature, are observed by photoluminescence (PL) spectra at low temperature in this study. The PL spectra peaks of the interband transitions from 2DEG subbands to the valence band are in the range from 3.486 to 3.312 eV. The effects of the strain caused by different Al fractions of the top layer, and that of the spacer thickness on the 2DEG phenomena are discussed. Redshifts due to temperature variations for various HEMT structures are observed in 2DEG subbands and in the band-edge emission, which is believed to be evidence of interband transitions from 2DEG subbands to valence bands.

The convergence of longitudinal excitons onto the Γ5transverse exciton in GaN and the thermal activation energy of longitudinal excitons

“…The temperature dependent PL spectra (K c) are shown in figure 2. Here, two transverse free excitons 5 and 6 dominate the spectra with transition energies of 3.490 eV and 3.484 eV, respectively at temperature of 10 K. The separation between the two free excitons is 5.9 meV, in excellent agreement with Fang et al [20] report for a similar structure; Al 0.15 Ga 0.85 N/GaN heterostructure grown on (0001) sapphire by metal organic chemical vapor deposition (MOCVD). They reported photon energies of 3.492 eV and 3.486 eV for 5 and The spectra are displaced vertically for clarity.…”

“…They collapsed at faster rate than the free excitons as the temperature increases. This behavior including the position, separation and intensity relative to 6 are comparable to those reported in [20,21,23] for donor-bound excitons. The two shoulders identified as two donor-bound excitons D( 5) and D( 6) associated with the free excitons 5 and 6 , respectively, since higher temperatures free bound excitons thus creating free excitons and free donors [37].…”

Ultraviolet and visible micro‐Raman and micro‐photoluminescence spectroscopy investigations of stress on a 75‐mm GaN‐on‐diamond wafer

“…The GaN/D PL spectrum in Fig. 4(a) is similar to what has been previously reported in room temperature GaN measurements [17,22,24,29,35,36] confirming the high quality of the GaN. A shift in peak energy between each curve, as seen in the graph, is attributed to the difference in stress observed when comparing the surface and interface of the GaN layer using UV micro-Raman.…”

Surface photovoltage spectroscopy of epitaxial structures for high electron mobility transistors

“…Such a methodology should be contactless, nondestructive, wafer-scalable, and usable for structures with different material compositions. Indeed, photoluminescence 5,6 electroreflectance, photoreflectance, 7 and x-ray microscopy 8 have been used for the characterization of HEMT structures.…”