We studied on rf molecular beam epitaxy (RF-MBE) growth of AlInN ternary alloys on N-polarity GaN templates. The growable highest temperature for the AlInN ternary alloy with mid-composition range was about 600 °C, which was very similar to that of N-polarity InN epitaxy. The compositional and structural qualities of AlInN ternary alloys were quite poor, however, for growth temperatures above 580 °C. AlInN ternary alloys without apparent phase separation in the whole composition range could be grown at 550 °C, and their crystalline, electrical, and optical properties were characterized. The bowing parameter for the optical bandgap of AlInN ternary alloys was found to be 4.96±0.28 eV. Further we for the first time fabricated InN/AlInN multiple quantum wells (MQWs).

PACS 71.20.Nr, 78.20.Ci, 78.55.Cr InN crystals are grown on sapphire substrates by a plasma assisted MBE system. The carrier concentration of the samples are 2×10 18 −1×1019 cm -3. Optical transmission and reflectance measurements are performed on these samples in a temperature range of 8 -300 K. The resultant spectra are analysed by theoretical spectra based on a LO-phonon plasmon coupling scheme for phonon related factor and nonparabolic conduction band structure for electronic transition factor. The observed absorption edge is estimated to mainly originate from the valence band to conduction band transition rather than defect or impurity related transition on the basis of the electron concentration dependence of the momentum matrix element. The bandgap energy is about 0.63 eV, and increases with the temperature decrease.

The effects of substrate temperature and surface stoichiometry on the growth behavior of InN were investigated in molecular beam epitaxy with in situ monitoring by reflection high-energy electron diffraction and spectroscopic ellipsometry. InN was grown on nitrided sapphire substrate or N-polarity GaN template. For both cases, InN layers were found in N polarity by coaxial impact collision ion scattering spectroscopy. At growth temperatures ranging from 470 to 590 C, the N-rich condition was favorable for stable InN growth. Under the In-limited growth condition, the stepflow growth of InN was achieved on N-polarity GaN template at 580 C with a growth rate of 1.3 mm/h. The FWHMs of X-ray rocking curves around InN (002) and (102) Introduction InN, as an important III-nitride semiconductor, is attracting much attention with regard to extending the working wavelength of optoelectronic devices up to the orange and red region, as well as to developing high-frequency and high-power/ temperature electronic devices [1,2]. Compared with GaN and AlN, InN has the smallest effective electron mass, exhibits the highest peak drift velocity and has a peak overshoot velocity that lasts over the longest distances [2,3]. InN is expected to be a more suitable material for electronic devices such as high electron mobility transistors. However, InN has been less studied compared with GaN and its related alloys. To improve InN layer quality, several techniques have been tried, such as migration-enhanced epitaxy and the use of AlN buffer layers and GaN intermediate layers, but thick InN epilayers with high-quality and atomically flat surfaces are still difficult to achieve [4,5]. For molecular beam epitaxy (MBE) growth, substrate temperature and surface stoichiometry are two of the most important factors. In III-nitride systems we must also consider the significant effects of polarity on the epitaxy process.In the present work, the dependence of InN growth behavior on substrate temperature and surface stoichiometry was investigated in radio frequency plasma-assisted MBE. High crystal quality InN layers with good electrical properties were obtained on MBE-grown N-polarity GaN template.Step flow growth morphologies were observed even when the InN growth rate was as high as 1.3 mm/h. It was clearly shown that the InN layers were grown in N polarity.

The radiation properties of a GaN/AlGaN‐based terahertz‐quantum cascade laser (THz‐QCL) device fabricated on a high quality GaN substrate were investigated in this work. The radiant intensity from a THz‐QCL fabricated on a GaN substrate showed a value (∼20 pW) about 10 times higher than that from a THz‐QCL grown on a metal organic chemical vapor deposition (MOCVD)‐GaN template that we had used before. Furthermore, we observed for the first time spontaneous THz emission with a peak at 1.37 THz in the case of a THz‐QCL grown on a GaN substrate. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Carrier transport in GaN terahertz (THz) quantum cascade laser (QCL) structures is theoretically investigated using a non-equilibrium Green's function method. Although scattering due to polar optical phonons in GaN is greatly enhanced with respect to GaAs/AlGaAs THz QCLs, the phonon-induced broadening of the laser levels is found to remain much smaller than other sources of broadening arising from impurity and electron-electron scattering. The gain is calculated self-consistently accounting for the correlation effects in level broadening. Three-well based design with resonant-phonon scheme shows a peak gain of 88/cm at 10 K, and 34/cm at 280 K, which remains above the calculated loss of a double metal waveguide. The results suggest that lasing at 6.6 THz, which is beyond the traditional GaAs THz QCLs, is possible up to 280 K.