Full-wafer stress mapping is accomplished using visible and ultraviolet (UV) micro-Raman spectroscopy of a 730-nm thick GaN layer integrated with diamond grown by chemical vapor deposition. The UV measurements taken from both sides of the wafer reveal a higher tensile stress of 0.86 6 0.07 GPa at the free GaN surface compared to 0.23 6 0.06 GPa from the GaN/diamond interface, each with good cross-wafer uniformity. Factors influencing the overall stress and stress gradient are understood based on relaxation from dislocations in the GaN which vary in density along the growth direction. Simulations incorporating a model for stress relaxation in the GaN elastic modulus adequately describe the observed dependence. Published by AIP Publishing.

Direct measurements of self-heating in gallium nitride (GaN) transistor using ultraviolet (UV) and visible micro-Raman spectroscopy are reported. The material stack was grown on silicon substrates and consists of an AlN nucleation, AlGaN transition, GaN buffer, and AlGaN barrier layers. Phonon shifts are used to estimate the temperature rise. UV measurements probe the current-carrying 2-D electron gas (2-DEG) in the GaN near the interface with the barrier region. Visible micro-Raman measurements provide an average temperature rise through GaN, AlN, and substrate near its interface with AlN. Together, these measurements provide a temperature depth profile. Under identical drive conditions, the increase in temperature from UV micro-Raman is approximately twice what is obtained from the visible measurements, reaching as high as 350°C above ambient temperature at input power of 7.8 W/mm. The temperature depth profile is simulated using finite-element analysis. We find that the temperature dependence of the thermal conductivity of GaN is important to incorporate in these simulations due to the large temperature rise in the 2-DEG region. A thermal boundary resistance of 1 × 10 −8 K · m 2 /W is obtained from the combined simulation and experimental results.

Polycrystalline diamond stripes, with a nominal thickness of $1.5 lm and various widths, were selectively grown on silicon substrates using chemical vapor deposition. Stress measurements using ultraviolet micro-Raman mapping reveal high compressive stress, up to $0.85 GPa, at the center of the diamond stripe, and moderate tensile stress, up to $0.14 GPa, in the substrate close to the interface with the diamond. Compressive stresses on diamond decrease with diminishing stripe widths. The stress map is well-described using finite element simulation incorporating solely thermal expansion effects.

Double heterostructures (DH) were produced consisting of a CdTe film between two wide band gap barriers of CdMgTe alloy. A combined method was developed to quantify radiative and non-radiative recombination rates by examining the dependence of photoluminescence (PL) on both excitation intensity and time. The measured PL characteristics, and the interface state density extracted by modeling, indicate that the radiative efficiency of CdMgTe/CdTe DHs is comparable to that of AlGaAs/GaAs DHs, with interface state densities in the low 1010 cm−2 and carrier lifetimes as long as 240 ns. The radiative recombination coefficient of CdTe is found to be near 10−10 cm3s−1. CdTe film growth on bulk CdTe substrates resulted in a homoepitaxial interface layer with a high non-radiative recombination rate.

Heterostructures with CdTe and CdTe1-xSex (x ∼ 0.01) absorbers between two wider-band-gap Cd1-xMgxTe barriers (x ∼ 0.25–0.3) were grown by molecular beam epitaxy to study carrier generation and recombination in bulk materials with passivated interfaces. Using a combination of confocal photoluminescence (PL), time-resolved PL, and low-temperature PL emission spectroscopy, two extended defect types were identified and the impact of these defects on charge-carrier recombination was analyzed. The dominant defects identified by confocal PL were dislocations in samples grown on (211)B CdTe substrates and crystallographic twinning-related defects in samples on (100)-oriented InSb substrates. Low-temperature PL shows that twin-related defects have a zero-phonon energy of 1.460 eV and a Huang-Rhys factor of 1.50, while dislocation-dominated samples have a 1.473-eV zero-phonon energy and a Huang-Rhys factor of 1.22. The charge carrier diffusion length near both types of defects is ∼6 μm, suggesting that recombination is limited by diffusion dynamics. For heterostructures with a low concentration of extended defects, the bulk lifetime was determined to be 2.2 μs with an interface recombination velocity of 160 cm/s and an estimated radiative lifetime of 91 μs.