The dislocation structure and photoluminescence of partially relaxed Si 1−x Ge x layers on Si(001) substrates were studied to reveal the contribution from dislocations localized in different regions of the heterostructure (SiGe layer, SiGe/Si interface, Si substrate) to the dislocation-related PL. The D1 and D2 lines were ascribed to products of dislocation reactions in intersection sites. The known dependence of the D4 line spectral position on the Ge content is not observed, which is explained by the effect of elastic strain in the SiGe/Si heterostructure.

The electrical and structural properties of AlN/GaN heterostructures grown by molecular beam epitaxy on sapphire are compared with those of AlGaN/GaN heterostructures. The structural characteristics as assessed by x-ray diffraction show little difference but the electron density in the two-dimensional electron gas is about twice higher for AlN/GaN structures with only slightly lower mobility than in AlGaN/GaN. By proper choice of the Fe doping in GaN(Fe) and the thickness of unintentionally doped GaN layers, the composite buffer of the structure can be made semi-insulating. The current through the AlN/GaN structures is determined by tunneling through the AlN barrier and is much higher than that for AlGaN/GaN films due to the lower thickness of AlN compared to AlGaN. Increasing the thickness of AlN from 3 to 4 nm decreases the leakage current by about an order of magnitude.

Structural and electrical properties of nonpolar m-GaN films grown on m-SiC using standard metalorganic chemical vapor deposition (MOCVD) and two versions of sidewall epitaxial lateral overgrowth were studied. It is shown that lateral overgrowth allows one to dramatically reduce the dislocation density from over 109 cm−2 to ∼107 cm−2. In good correlation with that we observed a strong reduction in the density of electron traps Ec−0.25 eV and Ec−0.6 eV from over 1015 cm−3 to ∼1014 cm−3, respectively, in MOCVD m-GaN and in laterally overgrown m-GaN. Preliminary studies of the effects of changing the V/III ratio and of Si doping were performed. The MOCVD m-GaN films grown with high V/III ratio of 1000 were semi-insulating, with the Fermi level pinned near the 0.6 eV traps. Decreasing the V/III value to 250 shifted the Fermi level upward, close to the level of the 0.25 eV traps. Si doping in laterally overgrown samples strongly suppressed the formation of major electron traps but enhanced the formation of hole traps near Ev+0.9 eV. We also report on electrical properties of the GaN interface with the AlN buffer used to facilitate good quality growth on SiC. These properties are dominated by a high concentration of 0.15 eV traps.

The electrical properties of AlGaN∕GaN high electron mobility transistor structures grown on composite GaN(Fe)∕GaN buffers by molecular beam epitaxy were reported. The concentration of Fe in the GaN(Fe) layer ranged from 8×1016to3×1017cm−3 as established by secondary ion mass spectrometry. The thickness of the undoped GaN layer of the buffer was varied from 2.2to4.1μm. For thinner buffers and higher Fe concentration, the buffer was semi-insulating, with the Fermi level pinned near Ec-0.57eV. For thicker buffers and lower Fe concentration, the top part of the buffer was conducting. Admittance spectra measured in conducting buffers also showed a prominent contribution from Ec-(055–0.6)eV electron traps. Despite the universal prominence of these traps in all our films, the behavior of their concentration with Fe doping and with increased distance from the GaN (Fe)∕GaN boundary is not compatible with the assumption that they are due to substitutional Fe acceptors. Possible compensation mechanisms in the studied structures were discussed.

Semi-insulating GaN͑Fe͒ films grown by molecular beam epitaxy ͑MBE͒ were characterized by measuring electrical properties, deep-level spectra, Fe distribution profiles, microcathodoluminescence ͑MCL͒ spectra, electron-beam-induced current, and MCL imaging. The films were high-quality GaN͑Fe͒ with Fe concentration from ϳ3 ϫ 10 16 to ϳ 3 ϫ 10 17 cm −3 . The resistivity of GaN͑Fe͒ buffers was Ͼ10 5 ⍀ cm, with the Fermi level pinned near E c 0.5 eV. The buffer quality was characterized for Si-doped GaN and AlGaN/GaN transistor structures grown by MBE on GaN͑Fe͒. In contrast to the reported results for growth by metallorganic chemical vapor deposition, Fe distribution profiles did not show long tails extending into the layers grown on top of GaN͑Fe͒. No features attributed to Fe were observed in lightly doped n-GaN grown on GaN͑Fe͒ buffers. The n-GaN films showed electron mobility of Ͼ500 cm 2 /V s. AlGaN/GaN transistor structures grown on GaN͑Fe͒ buffers showed two-dimensional electron gas mobility Ͼ1900 cm 2 /V s at 300 K, with a sheet density ϳ1 ϫ 10 13 cm −2 and a good pinch-off and a low interdevice leakage.