Effects of alloying and hydrostatic pressure on electronic and optical properties of GaAs-AlxGa1-xAs superlattices and multiple-quantum-well structures

The exceptionally high thermal conductivity after 'alloying' two-dimensional gallium nitride (GaN) and aluminum nitride (AlN)

Alloying is a widely employed approach for tuning properties of materials, especially for thermal conductivity which plays a key role in the working liability of electronic devices and the energy conversion efficiency of thermoelectric devices. Commonly, the thermal conductivity of an alloy is acknowledged to be the smallest compared to the parent materials. However, the findings in this study bring some different points of view on the modulation of thermal transport by alloying. The thermal transport properties of monolayer GaN, AlN, and their alloys of Ga _x Al_1-x N are comparatively investigated by solving the Boltzmann transport equation (BTE) based on first-principles calculations. The thermal conductivity of Ga_0.25Al_0.75N alloy (29.57 Wm^-1 K^-1) and Ga_0.5Al_0.5N alloy (21.49 Wm^-1 K^-1) are found exceptionally high to be between AlN (74.42 Wm^-1 K^-1) and GaN (14.92 Wm^-1 K^-1), which violates the traditional knowledge that alloying usually lowers thermal conductivity. The mechanism resides in that, the existence of Al atoms reduces the difference in atomic radius and masses of the Ga_0.25Al_0.75N alloy, which also induces an isolated optical phonon branch around 18 THz. As a result, the scattering phase space of Ga_0.25Al_0.75N is largely suppressed compared to GaN. The microscopic analysis from the orbital projected electronic density of states and the electron localization function further provides insight that the alloying process weakens the polarization of bonding in Ga_0.25Al_0.75N alloy and leads to the increased thermal conductivity. The exceptionally high thermal conductivity of the Ga _x Al_1-x N alloys and the underlying mechanism as revealed in this study would bring valuable insight for the future research of materials with applications in high-performance thermal management.

Crystallographic input data for (001)-, (110)- and (111)-oriented superlattices

General aspects concerned with (001)-, (110)- and (111)-oriented superlattices (SLs) have been investigated. In particular, the symmetry of these systems have been derived and given in detail. As a test, the obtained data have been utilized to calculate electronic structures and gaps of a standard GaAs/AlAs system using an accurate version of the first principle full potential linear muffin-tin orbital (FPLMTO) method based on a local-density functional approximation (LDA).

Effects of hydrostatic pressure on the electron [Formula: see text] factor and g-factor anisotropy in GaAs-(Ga, Al)As quantum wells under magnetic fields

The hydrostatic-pressure effects on the electron-effective Landé [Formula: see text] factor and g-factor anisotropy in semiconductor GaAs-Ga(1-x)Al(x)As quantum wells under magnetic fields are studied. The [Formula: see text] factor is computed by considering the non-parabolicity and anisotropy of the conduction band through the Ogg-McCombe effective Hamiltonian, and numerical results are displayed as functions of the applied hydrostatic pressure, magnetic fields, and quantum-well widths. Good agreement between theoretical results and experimental measurements in GaAs-(Ga, Al)As quantum wells for the electron g factor and g-factor anisotropy at low values of the applied magnetic field and in the absence of hydrostatic pressure is obtained. Present results open up new possibilities for manipulating the electron-effective g factor in semiconductor heterostructures.