U. Kaufmann

Determination of the GaN/AlN band offset via the (/0) acceptor level of iron

A characteristic infrared luminescence spectrum, dominated by a zero‐phonon line at 1.30 eV, has been observed on AlN polycrystalline material. It is assigned to the spin‐forbidden internal 3d–3d transition 4T1(G)→6A1(S) of Fe3+Al(3d5). By photoluminescence excitation spectroscopy the (‐/0) acceptor level of iron in AlN could be located at EV+3.0 eV. The corresponding value for iron in GaN is EV+2.5 eV. From these values, the valence‐band offset in AlN/GaN heterojunctions is predicted as ΔEV=0.5 eV, the conduction‐band offset as ΔEC=2.3 eV.

Infrared luminescence of residual iron deep level acceptors in gallium nitride (GaN) epitaxial layers

A characteristic infrared luminescence band, dominated by a zero‐phonon line at 1.30 eV has been consistently detected in gallium nitride (GaN) epitaxial layers. It is assigned to the intra‐3d‐shell transitions 4T1(G)→6A1(S) of omnipresent iron trace impurities, Fe3+Ga(3d5). Another infrared emission is often also observed at 1.19 eV. This is tentatively assigned to chromium trace impurities, Cr4+Ga(3d2). The role of iron and chromium as minority‐carrier lifetime killers in GaN‐based optoelectronic devices is suggested from these data.

Photoluminescence of residual transition metal impurities in GaN

A large number of epitaxial GaN samples as well as AlN ceramics have been studied by photoluminescence (PL) and PL excitation spectroscopy. In addition to the PL of residual iron, two new bands with zero‐phonon‐lines at 0.931 and 1.193 eV have been observed frequently in GaN. An analysis of the PL bands indicates that they arise from internal transitions within the 3d shell of residual vanadium and chromium impurities. The chromium PL has also been observed in polycrystalline AlN ceramics.

Magnetic circular dichroism and electron spin resonance of the A− acceptor state of vanadium, V3+, in 6H-SiC

Abstract The magnetic circular dichroism (MCD) of the absorption has been studied in a 6H-SiC crystal highly contaminated with vanadium, V. In addition to previously reported MCD absorption lines of V 4+ (3d 1 ), new sharp MCD lines have been observed near 2.0 μm. The chemical nature and origin of these lines were identified by MCD-detected electron spin resonance. They arise from V 3+ (3d 2 ) and most likely correspond to the 3 A 2 → 3 T 2 crystal-field absorption. The positions of the V 3+ V 4+ acceptor level and the V 4+ V 5+ donor level are discussed. The possibility of growing high-resistivity SiC crystals by deliberate vanadium doping is pointed out.

Deep donor state of vanadium in cubic silicon carbide (3C‐SiC)

Electron spin resonance (ESR) of silicon‐substitutional vanadium in its neutral V4+Si (3d1) state has been observed in cubic bulk 3C‐SiC single crystals. By photo‐ESR the position of the (0/+) deep donor level of vanadium could be located at EV+1.7 eV. Using this level as common reference in 3C‐SiC and 6H‐SiC, the valence‐band discontinuity in the 3C‐SiC/6H‐SiC interface is predicted as ΔEV=0.1 eV, with the valence band of 3C‐SiC lying lower in energy. We also offer an explanation for the absence of intra‐3d‐shell infrared luminescence of V4+ (3d1) in 3C‐SiC.

Determination of the GaN/A1N band discontinuities via the (−0) acceptor level of iron

Abstract The 1.3 eV iron related emission bands in GaN and A1N were analysed by photoluminescence and photoluminescence excitation spectroscopy. The ( − 0 ) acceptor levels of iron in GaN and A1N were determined. A value of 0.5 eV for the GaN/A1N valence band discontinuity is deduced. Values for the GaAs/GaN and the GaAs/A1N valence band discontinuities are discussed.

Properties of Mg and Zn acceptors in MOVPE GaN as studied by optically detected magnetic resonance

Abstract We have studied the photoluminescence (PL) and optically detected magnetic resonance (ODMR) of undoped, n -doped and p -doped thin wurtzite GaN layers grown by metal-organic chemical vapor deposition on sapphire substrates. The ODMR data obtained for undoped. Mg-doped and Zn-doped GaN layers provide an insight into the recombination mechanisms responsible for the broad yellow (2.25 eV), the violet (3.15 eV) and the blue (2.8 eV) PL bands, respectively. The ODMR results for Mg and Zn also show that these acceptors do not behave effective mass like and indicate that the acceptor hole is mainly localized in the nearest neighbor shell surrounding the acceptor core. In addition concentration effects in heavily doped GaN:Mg have been studied.

Photoresponse of the EL2 absorption in undoped semi‐insulating GaAs

The response of the EL2 absorption band to monochromatic secondary illumination has been studied in undoped semi‐insulating GaAs. Photoinduced changes of the absorption band are spectrally nonuniform. In addition, the changes are nonmonotonic in time similar to the EL2 photocapacitance transients: A fast enhancement in absorption is followed by a slow quenching. These data can be explained in terms of the EL2 properties known from photocapacitance studies. A comparison with recent electron paramagnetic resonance (EPR) results for the AsGa antisite provides direct evidence that the EL2 absorption band and the As+Ga EPR are induced by the same defect.

New omnipresent electron paramagnetic resonance signal in as‐grown semi‐insulating liquid encapsulation Czochralski GaAs

Electron paramagnetic resonance studies on as‐grown semi‐insulating liquid encapsulation Czochralski (LEC) GaAs at 35 GHz have revealed a new resonance labeled FR3. It is consistently present in LEC material but usually unobservable in Bridgman samples, thus strongly indicating that the defect involved contains boron. The center has trigonal symmetry and is electrically active. Its spectrum indicates a d 9 or p5 one‐hole configuration. We tentatively identify FR3 with a Ga antisite complex, Ga−As ‐B0Ga.

Electrically and optically active molybdenum impurities in commercial SiC substrates

Abstract We report on the identification of optically and electrically active molybdenum impurities in commercial 6H- and 15R-SiC substrates by conventionally and optically detected magnetic resonance (ESR, ODMR) and magnetic circular dichroism (MCD) detection. Two impurity charge states, Mo4 + (4d2) and Mo3 +(4d3), are reported for both polytypes. We also observed the 3A2 → 3T2 crystal field absorptions of Mo4 + (4d2) in the 1.0–1.25 eV spectral range. Mo impurities on different inequivalent lattice sites in 6H- and 15R-SiC are resolved for the first time.