. Hg, 68.37.Hk, 68.55.Jk, 78.55.Cr, high In content (In-rich) InGaN was grown on R-plane (10-12) sapphire with an InN template by radio-frequency plasma assisted molecular beam epitaxy (RF-MBE). Nitridation of Rplane sapphire was carried out at 300 °C for 2 hours by RF-nitrogen plasma. A template of A-plane InN was grown at 400 °C. The In-rich InGaN films were then grown at the same temperature on the InN template. We characterized the films using reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), scanning electron microscopy (SEM) and photo-luminescence (PL). These results indicated clearly that non-polar In 0.71 Ga 0.29 N was successfully obtained with a PL emission at approximately 1.1 eV.

This paper describes our recent progress on InN, In‐rich Inx Ga1–x N, and InN/Inx Ga1–x N quantum wells (QWs) grown by radio‐frequency plasma‐assisted molecular‐beam epitaxy. Among the essential growth sequences to obtain high‐quality InN, the nitridation process of (0001) sapphire substrates was reexamined. It was found that the lower‐temperature and longer–period nitridation‐process was very effective in improving crystalline quality of InN films. We succeeded in dramatically improving c ‐axis orientation of InN films without deteriorating their a ‐axis orientation by nitridating the substrates at a relatively low‐temperature of 300 °C for a relatively long period of 2 h. The full widths at half maximum (FWHMs) of (0002) X‐ray rocking curves as narrow as 1 arcmin were obtained from only 400 nm thick InN films. These FWHMs are the narrowest value ever reported for InN and moreover approximately a twentieth part of the values obtained from our conventional InN films with a similar thickness, which were grown via the conventional nitridation process carried out at 550 °C for 1 h. Furthermore interference fringes in X‐ray diffraction (ω –2θ scan) were observed from these improved InN films. These high crystalline quality InN layers have been employed as a template for the growth of In‐rich Inx Ga1–x N layers (0.70 ≤ x ≤ 0.94). The resultant Inx Ga1–x N layers have shown dramatic improvements in not only the surface morphology but also both the a ‐ and c ‐axis orientations. By employing In0.8Ga0.2N layers of improved quality as the bottom barrier layer, InN/In0.8Ga0.2N multiple quantum well (MQW) and single quantum well (SQW) structures with different well widths were fabricated. Clear satellite peaks of X‐ray diffraction were observed from these MQW structures. Both of these SQW and MQW structures have exhibited a blue shift of the photoluminescence peak energy with decreasing well width. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

No abstract

No abstract

Thermoelectric (TE) devices are fabricated using AlGaN/GaN heterostructures, which are epitaxially grown on sapphire substrates by metal‐organic chemical vapor deposition. The epilayers are processed to form 3 × 3 mm2 square‐shaped TE devices. These devices include two‐dimensional electron gas produced by electric polarization discontinuity naturally formed at AlGaN/GaN interface, and thereby exhibit that Seebeck coefficients (S) are positively correlated with their carrier concentration (n) in n ≳ 4 × 1019 cm−3. In contrast, TE devices made from bulk materials generally exhibit a negative correlation between S and n.