Double-cross epitaxial overgrowth of nonpolar gallium nitride layers

Epitaxial gallium nitride (GaN) structures have been manufactured by the lateral overgrowth technology, whereby GaN epilayers are grown in stripe windows on a partly masked initial GaN layer. It is established that in addition to the traditional orientation of stripes across the c axis, the process is also possible for the stripes oriented at 45° relative to this axis. In this case, two lateral overgrowth processes in mutually perpendicular directions can be performed, which would significantly reduce the relative area of imperfect material formed over windows in the mask.     

InAlAs/InGaAs/InP High-Electron-Mobility Transistors with a Composite Channel and Higher Breakdown Characteristics

Technical Physics Letters - A high-electron-mobility transistor (HEMT) based on InAlAs/InGaAs/InP heterostructures possessing higher breakdown characteristics is developed. An InGaAs composite...     

Laser characteristics of an injection microdisk with quantum dots and its free-space outcoupling efficiency

The spectral, threshold, and power characteristics of a microdisk laser 31 μm in diameter with an active region based on InAs/InGaAs quantum dots, operating in the continuous-wave (cw) mode at room temperature are studied. The minimum threshold current density is 0.58 kA/cm², the subthreshold linewidth of the whispering-gallery mode is 50 pm at a wavelength lying in the range of 1.26–1.27 μm. The total power emitted into free space reaches ~0.1 mW in the cw mode, whereas the radiation power of the whispering-gallery modes is ~2.8%.     

Influence of the carrier Gas, trimethylgallium flow, and growth time on the character of the selective epitaxy of GaN

The influence of the carrier gas, trimethylgallium flow, and growth time on the character of the selective epitaxy of GaN in stripe windows oriented along the crystallographic direction 〈 $\bar 1$ 100〉 GaN for various widths of the mask between the stripes is studied. It is shown that the addition of nitrogen in the reactor atmosphere leads to changes in the form of the stripes in the case of wide (40 μm) mask from a rectangular form restricted by a {1 $\bar 1$ 20} lateral face to a trapezoidal form restricted by a {1 $\bar 1$ 22} lateral face. It is also shown that during growth in the nitrogen-hydrogen mixture, the gallium flow starts to considerably affect the form of the growing stripes. It is shown that the process is significantly unstable, which leads to a noticeable variation in the form type as the transverse section of the stripe increases.     

Properties of GaAsN nanowires grown by magnetron-sputtering deposition

The effectiveness of magnetron-sputtering deposition in an Ar-N₂ plasma-forming mixture as a technique for the fabrication of arrays of GaAs_{1 ? x} N _x nanowires (NWs) with typical diameters from 10 to 200 nm and lengths up to 3000 nm is demonstrated. Dependence of the growth character of NW on the parameters of the synthesis process, such as the size of Au droplets, deposition rate, and crystallographic orientation of the surface and the temperature of the substrate, is investigated. Analysis of the dependence of NW height on their diameter demonstrates that growth occurs predominantly by the diffusion mechanism. The nitrogen content is kept stable for growth temperatures in the range 400–500°C, being as high as 2.7%. For the substrate temperatures in the range 530–600°C, an abrupt drop in the nitrogen content in the alloy takes place. In the photoluminescence (PL) spectra of the samples obtained, a red shift of the emission band is observed, which is related to an increase in the nitrogen content. The growth-temperature dependence of the position of the luminescence band and the nitrogen content is determined. It is found that the PL intensity of samples with GaAsN NWs containing 2.7% nitrogen increases by a factor of 5–10 as compared to samples with planar layers, which is explained by the absence of structural defects in NWs.     

Laser generation at 1.3 μm in vertical microcavities containing InAs/InGaAs quantum dot arrays under optical pumping

The fundamental possibility of achieving temperature stability of laser emitters of 1.3-μm spectral range exhibiting a vertical microcavity and an active region based on InAs/InGaAs quantum dots (QDs) is investigated. It is demonstrated that using an undoped hybrid vertical optical microcavity formed by a lower undoped semiconductor and an upper distributed dielectric Bragg reflectors allows obtaining laser oscillation up to a temperature of ~100°C at nearly constant threshold optical pump power for an active region consisting of QD layers under optimal spectral mismatch between the position of maximum gain of the QD ground state and the resonance wavelength.     

Specific features of proton interaction with transistor structures having a 2D AlGaN/GaN channel

It has been shown that the interaction of 1 MeV protons at doses of (0.5–2) × 10¹⁴ cm^–2 with transistor structures having a 2D AlGaN/GaN channel (AlGaN/GaN HEMTs) is accompanied not only by the generation of point defects, but also by the formation of local regions with a disordered nanomaterial. The degree of disorder of the nanomaterial was evaluated by multifractal analysis methods. An increase in the degree of disorder of the nanomaterial, manifested the most clearly at a proton dose of 2 × 10¹⁴ cm^–2, leads to several-fold changes in the mobility and electron density in the 2D channel of HEMT structures. In this case, the transistors show a decrease in the source–drain current and an order-of-magnitude increase in the gate leakage current. In HEMT structures having an enhanced disorder of the nanomaterial prior to exposure to protons, proton irradiation results in suppression of the 2D conductivity in the channel and failure of the transistors, even at a dose of 1 × 10¹⁴ cm^–2.     

Synthesis of GaN nano- and microwire crystals induced by a titanium nanolayer

The possibilities of a new method of growing gallium nitride nano- and microwire crystals using continuous titanium films with a thickness of 10–30 nm during growth are described. It is shown that this method can provide growth of high-quality GaN nanowire crystals at an extremely high rate of about 10 μm/min.     

Single-spatial-mode semiconductor VCSELs with a nonplanar upper dielectric DBR

Single-spatial-mode semiconductor vertical-cavity surface-emitting lasers (VCSELs) with a non-planar upper (output) dielectric distributed Bragg reflector (DBR) for the 850 nm spectral region are fabricated. The suggested design provides stable single-mode generation in the entire range of working currents, limited by overheating of the active region. Devices with intracavity contacts and a comparatively large current-aperture diameter (5–6 μm) exhibit single-mode lasing at a wavelength of 840–845 nm in the continuous-wave mode at room temperature with threshold currents of 1.2–1.3 mA, a differential efficiency of 0.5–0.55 mW mA^?1, and anoutput power of up to 2 mW.