Growth of high-quality Bi 2 Se 3 films is crucial not only for study of topological insulators but also for manufacture of technologically important materials. We report a study of the heteroepitaxy of single-crystal Bi 2 Se 3 thin films grown on GaAs and InP substrates by use of molecular beam epitaxy. Surface topography, crystal structure, and electrical transport properties of these Bi 2 Se 3 epitaxial films are indicative of highly c-axis oriented films with atomically sharp interfaces.

The authors investigate the structural properties of Bi2Se3 and Bi2Te3 topological insulator layers grown on sapphire (0001) substrates by molecular beam epitaxy, using various pregrowth optimization methods. Samples of Bi2Se3 grown on sapphire with a particular combination of pregrowth surface treatment steps showed evidence of greatly reduced twinning and significantly reduced surface roughness. Evidence of twinning, and its suppression by the appropriate choice of pregrowth steps, is obtained from x-ray diffraction Φ-scan measurements as well as atomic force microscopy (AFM) images. Improved surface roughness is also evident from the AFM images. Growth of Bi2Te3 on sapphire exhibited similar reduced twinning by the application of the pregrowth surface preparation steps, although the surface roughness was significantly greater than that of Bi2Se3. Additional improvements in surface roughness of the Bi2Te3 were achieved by growing the Bi2Te3 on a Bi2Se3 buffer layer.

The rapid emergence of gallium-nitride (GaN) light-emitting diodes (LEDs) for solid-state lighting has created a timely opportunity for optical communications using visible light. One important challenge to address this opportunity is to extend the wavelength coverage of GaN LEDs without compromising their modulation properties. Here, a hybrid source for emission at 540 nm consisting of a 450 nm GaN micro-sized LED (micro-LED) with a micron-thick ZnCdSe/ZnCdMgSe multi-quantum-well color-converting membrane is reported. The membrane is liquid-capillary-bonded directly onto the sapphire window of the micro-LED for full hybridization. At an injection current of 100 mA, the color-converted power was found to be 37 μW. At this same current, the −3 dB optical modulation bandwidth of the bare GaN and hybrid micro-LEDs were 79 and 51 MHz, respectively. The intrinsic bandwidth of the color-converting membrane was found to be power-density independent over the range of the micro-LED operation at 145 MHz, which corresponds to a mean carrier lifetime of 1.9 ns.

Access to charge transport through Dirac surface states in topological insulators (TIs) can be challenging due to their intermixing with bulk states or nontopological two-dimensional electron gas (2DEG) quantum well states caused by bending of electronic bands near the surface. The band bending arises via charge transfer from surface adatoms or interfaces and, therefore, the choice of layers abutting topological surfaces is critical. Here we report molecular beam epitaxial growth of Bi2Se3/ZnxCd1–xSe superlattices that hold only one topological surface channel per TI layer. The topological nature of conducting channels is supported by π-Berry phase evident from observed Shubnikov de Haas quantum oscillations and by the associated two-dimensional (2D) weak antilocalization quantum interference correction to magnetoresistance. Both density functional theory (DFT) calculations and transport measurements suggest that a single topological Dirac cone per TI layer can be realized by asymmetric interfaces: Se-terminated ZnxCd1–xSe interface with the TI remains “electronically intact”, while charge transfer occurs at the Zn-terminated interface. Our findings indicate that topological transport could be controlled by adjusting charge transfer from nontopological spacers in hybrid structures.

We report on the experimental demonstration of a ZnCdSe/ZnCdMgSe-based short-wavelength photovoltaic Quantum Cascade Detector (QCD). The QCD operates in two spectral bands centered around 2.6 μm and 3.6 μm. Calibrated blackbody measurements yield a peak responsivity of 0.1 mA/W or 2400 V/W at 80 K, and a corresponding 300 K background radiation limited infrared performance detectivity (BLIP) of ∼2.5 × 1010 cm √Hz/W. Comparison of background illuminated and dark current-voltage measurements demonstrates a BLIP temperature of 200 K. The device differential resistance-area product, decreases from about 106 Ω cm2 at 80 K to about 8000 Ω cm2 at 300 K, indicative of the ultra-low Johnson noise in the detectors.