GaN homoepitaxial layers grown by metalorganic chemical vapor deposition

Abstract

GaN homoepitaxial layers were grown using metalorganic chemical vapor deposition on the highly conductive GaN bulk crystals grown at high hydrostatic pressure. The epitaxial growth process was monitored by reflectivity of red laser light. The oscillations of its intensity served for the precise evaluation of the growth rate. The layers were then investigated using far-infrared reflectivity (FIR), x-ray diffraction, and photoluminescence. The FIR spectrum gave small free-electron concentration in the layers in contrast to the substrates which had about 2.5×1019 cm−3 of free electrons. In x-ray diffraction, the peaks of the substrate and of the layer were separated due to the difference between the lattice parameters of the bulk GaN substrate (expanded by free electrons and point defects) and the layer which had a low free electron concentration. Both peaks had rocking curves with half widths of about 20 arcsec. The photoluminescence spectrum contained narrow peaks of less than 1 meV with the excitonic lines well resolved. The spectrum was dominated by the donor-bound exciton peak. All acceptor-related peaks had small intensities that indicated a very low acceptor concentration in the layers.

Magnetic resonance studies of defects in GaN with reduced dislocation densities

“…As observed by other groups [16][17][18], high-resolution PL studies confirmed the high-crystalline quality of our undoped and Si-doped GaN homoepitaxial layers [19]. In particular, the Si-doped homoepitaxial sample exhibits sharper excitonic PL (linewidthsp1 meV) compared to that reported previously for GaN grown on Al 2 O 3 with similar Si doping levels [20].…”

“…Though not nearly as sharp as the excitonic PL observed from undoped GaN homoepitaxial layers with linewidths of B0.1 meV [16][17][18][19], the bandedge emission from these free-standing (thick) HVPE GaN templates is characterized by linewidths less than 1 meV [14]. An example of a high-resolution PL spectrum obtained at 5 K that demonstrates the high crystallinity of this material is shown in the inset of Fig.…”

High electron mobility in AlGaN/GaN heterostructures grown on bulk GaN substrates

“…These crystals were tested to be semi-insulating with a perfect crystallographic structure. 7 Prior to growth, the ͑0001͒ Ga face, which was found to be the best face polarity for a homoepitaxial layer, 8 as the nitrogen precursor and the group-III element were provided by standard solid-source effusion cells. An unintentionally doped GaN layer of about 1 m was grown at 800°C on a Mg-doped GaN single crystal, followed by a 200-Å-thick AlGaN layer.…”

GaN–AlGaN heterostructure field-effect transistors over bulk GaN substrates

“…6,7 This leads to photoluminescence spectra with very well-resolved excitonic transition lines of widths below 1 meV. 8 Recently, Mg-doped high-pressure-grown bulk GaN crystals were shown to be semi-insulating with perfect crystallographic structure.…”