Piezoelectric AlGaN/GaN FETs on SiC with high carrier mobility have been fabricated yielding IDS=450 mA/mm and gm=200 mS/mm. In the on-state, under UV-illumination, the devices sustain a drain voltage of VDS=49 V, corresponding to a power dissipation of 26.5 W/mm. On turn-on of the device from the pinch-off state, a significant delay in the drain current build-up is observed. This effect depends on the pinch-off time and the pinch-off voltage and can be removed by either a brief UV-illumination or a VDS>25 V applied in the on-state. The drain current transients are characterized by a relaxation time τ, which is in the order of several hundred seconds. From the temperature dependence of τ, an activation energy of about 280 meV and a capture cross section of 4.4·10−18cm2 were determined. The devices show pronounced persistent photoconductivity (PPC) and the drain current ID is sensitive to illumination.

We report on highly resolved photoluminescence (PL) and reflectance (RF) spectra of a homoepitaxial GaN layer grown by metal-organic vapor phase epitaxy. This sample exhibits narrow linewidths of several PL emission peaks, down to approximate to 100 mu eV full width at half maximum for some bound exciton transitions. As a consequence, we have detected new PL features as, e.g., a fivefold fine structure of the donor-bound exciton line at approximate to 3.471 eV, and other known PL transitions could be determined with high precision. In RF measurements, the extraordinary quality of the epitaxial layer allowed observation of weakly damped excitonic groundstate transitions and of narrow excited exciton transitions with high signal-to-noise ratio. [S0163-1829(99)14027-X].

Carefully optimized low-pressure metalorganic vapor phase epitaxy is used for homoepitaxial growth on distinctively pretreated GaN bulk single crystal substrates. Thereby, outstanding structural and optical qualities of the material have been achieved, exhibiting photoluminescence linewidths for bound excitons as narrow as 95 μeV. These extremely sharp lines reveal fine structures, not reported for GaN. Additionally, all three free excitons as well as their excited states are visible in low-temperature photoluminescence at 2 K. These transitions are clearly identified by reflectance measurements. X-ray diffraction analysis of these layers reveal about 20 arcsec linewidth for the (0004) reflex using CuKα radiation.

Piezoelectric AlGaN/GaN FETs with high carrier mobility have been fabricated yielding I-DS = 450 mA/mm and g(m), = 200 mS/mm. Upon turn-on of the device from the pinch-off state a significant delay in the drain current build-up is observed. This effect depends on the pinch-off time and the pinch-off voltage and can be removed by either a brief UV-illumination or a V-DS > 25 V applied in on-state. The relaxation time tau of this effect is of the order of several hundred seconds. From the temperature dependence of t an activation energy Of about 280 meV and a capture cross section of 4.4 x 10(-18) cm(2) can be extracted.

Electroreflectance spectroscopy was used to measure the direct transitions in strained Si1−xGex layers in the energy range from 3–6 eV. We were able to detect the transitions E1, E1 + Δ1, E′0, E0, E0 + Δ0, E2(X), E2(Σ) and E′1 for multiple samples with germanium concentrations from 12.5–28.1% for temperatures from 10–300 K. The transitions E1 + Δ1, E0, E0 + Δ0, E2(Σ) and E′1 were detected for the first time in strained Si1−xGex layers and it was also the first investigation of the temperature dependence of direct transitions in strained Si1−xGex. Good agreement with theoretical calculations of strain shifts was found for the E0 transition, while deviations occur for the E1 transition.