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We investigate band-gap tuning of bilayer graphene between hexagonal boron nitride sheets, by external electric fields. Using density functional theory, we show that the gap is continuously tunable from 0 to 0.2 eV, and is robust to stacking disorder. Moreover, boron nitride sheets do not alter the fundamental response from that of free-standing bilayer graphene, apart from additional screening. The calculations suggest that the graphene-boron nitride heterostructures could provide a viable route to graphene-based electronic devices.

We report the device performance of normal-incidence (In, Ga)As/GaAs quantum dot intersubband infrared photodetectors. A primary intersubband transition peak is observed at the wavelength of 13 μm (E0→E1) and a secondary peak at 11 μm (E0→E2). The measured energy spacing in the conduction band of the quantum dots is in good agreement with low temperature photoluminescence measurement and calculations. A peak detectivity of 1×1010 cm Hz1/2/W at 13 μm was achieved at 40 K for these devices.

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The group III-nitride (InN, GaN, and AlN) class of semiconductors has become one of two that are critical to a number of technologies in modern life—the other being silicon. Light-emitting diodes made from (In,Ga)N, for example, dominate recent innovations in general illumination and signaling. Even though the (In,Ga)N materials system is fairly well established and widely used in advanced devices, challenges continue to impede development of devices that include aluminum-containing nitride films such as (Al,Ga)N. The main difficulty is efficient doping of films with aluminum-rich compositions; the problem is particularly severe for p-type doping, which is essential for Ohmic contacts to bipolar device structures. This review briefly summarizes the fundamental issues related to p-type doping, and then discusses a number of approaches that are being pursued to resolve the doping problem or for circumventing the need for p-type doping. Finally, we discuss an approach to doping under liquid-metal-enabled growth by molecular beam epitaxy. Recent results from a number of groups appear to indicate that p-type doping of nitride films under liquid-metal-enabled growth conditions might offer a solution to the doping problem—at least for materials grown by molecular beam epitaxy.

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We have measured the optical and electrical properties of a five-period normal-incidence (In, Ga)As/GaAs quantum-dot infrared photodetector. A primary intersubband transition peak is observed at the wavelength of 10.2 μm and a secondary one at 9.4 μm. Excellent electron transport and peak detectivity of 7×109 cm Hz1/2/W are achieved at 30 K, with a low bias responsivity of up to 70 mA/W at 0.6 V. We believe that an observed avalanche gain process is initiated by intersubband absorption in the quantum dots. The maximum responsivity due to this avalanche multiplication process is about 4 A/W at a bias of 1.0 V.

A self-consistent, coupled optoelectronic simulation model is used to study microcavity GaN nanowire lasers. This model is applied to show that it is possible to design a nanowire laser with distributed-Bragg-reflector mirrors. Several advantages are expected to be enjoyed from the use of such mirrors. These include reduction of lasing threshold current density (or pumping density rate), dramatic reduction of cavity losses, and the achievement of stable, single-mode operation.