The optical band gap of hexagonal boron nitride (h‐BN) epitaxial film is investigated by means of transmittance and reflectance measurements. We grew the h‐BN epitaxial film on c‐plane sapphire substrate by metalorganic vaper phase epitaxy. X‐ray diffraction and reflection high‐energy electron diffraction reveal that the h‐BN epitaxial film has a smooth surface, and the epitaxial relationship is found to be (0001)h‐BN|| (0001)sapphire with an in‐plane orientation relationship of [11$ \bar 2 $0]h‐BN|| [1$ \bar 1 $00]sapphire. The photon energy dependence of the squared absorption coefficient is linear, indicating a direct band gap in the h‐BN, and the optical band gap is determined to be 5.9 eV. The single‐phase h‐BN epitaxial film provides a more intrinsic value of the optical band gap than the values estimated for polycrystalline or pyrolytic BN. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Influence of rapid thermal annealing on a 30 stack InAs/GaAs quantum dot infrared photodetector J. Appl. Phys. 94, 5283 (2003); 10.1063/1.1609634Effect of Be doping on the absorption of InGaAs/AlGaAs strained quantum-well infrared photodetectors grown by molecular-beam epitaxyWe studied the quantum wire photodetector ͑QRIP͒ structures with an InGaAs quantum wires ͑QWRs͒ active region formed by the strain-induced lateral ordering ͑SILO͒ process. The InGaAs multiple layer QWR structure maintains a small total strain due to the strain-balanced nature of the SILO process. The effects of growth temperature and layer structures on the QWR formation are studied using photoluminescence and transmission electron microscope measurements. High-resolution x-ray diffraction studies on QRIP structures consisting of 20 QWR layers confirmed the strain-balanced property of SILO-based structures.

We report a 20-layer In x Ga 1−x As/ In 0.52 Al 0.24 Ga 0.24 As quantum wire infrared photodetector grown on ͑001͒-axis InP substrate by molecular beam epitaxy. High density InGaAs quantum wires were formed, utilizing the strained-induced lateral-layer ordering process by growing a strain-balanced ͑GaAs͒ 1.80 / ͑InAs͒ 2.35 short-period superlattice. This device shows a unique polarized photoresponse which favors the normal-incident infrared radiation polarizing perpendicular to the wire orientation. The photoresponse at 6.3 m exhibited a peak detectivity of 3.13ϫ 10 9 cm Hz 1/2 / W at 10 K.

In this letter, a nonlithographic method for fabrication of high-quality site-controlled InAs quantum dots on GaAs is explored. The self-organized pores in nanochannel alumina (NCA) are used to define the nucleation sites of the site-controlled quantum dots. The pattern from the NCA is transferred to the GaAs substrate by electrochemical etching. The first layer of regrown InAs dots preferentially locate at the bottom of the etch pits on the GaAs substrate. Furthermore, cross-sectional transmission electron microscopy shows that when multiple layers of InAs dots are regrown, the dots will exhibit vertical alignment. To show the excellent optical quality of the regrown quantum dots, photoluminescence spectra are studied; room-temperature photo luminescence from the regrown dots is achieved.