We report on the characterization of wide-band-gap heterojunction diodes based on the p-ZnO/n-GaN material system. The layer structure consists of 11 µm GaN on sapphire substrates and As-doped ZnO film of thickness 0.4 µm obtained by plasma-assisted molecular beam epitaxy (PA-MBE). The quality of the heterojunction was examined by x-ray diffraction, atomic force microscopy and scanning electron microscopy. The arsenic concentration in ZnO, measured by secondary ion mass spectroscopy (SIMS), is 5 × 10²⁰ cm⁻³. The maximum forward-to-reverse current ratio I _F/I _R is of about 10⁵ in the applied voltage ±3 V, a very good result for this type of heterojunction.

Laplace transform deep level transient spectroscopy was used to study the acceptor levels of platinum and gold diffused into dilute (0– $5\%$ Ge) SiGe alloys. We show that Ge atoms in the first and in the second shell of atoms surrounding the impurity perturb the electronic properties of the Au and Pt acceptor defects. The magnitude of the splitting caused by one Ge atom in the first shell is $\sim 35\mathrm{meV}$ in both cases. The spectral distributions indicate an overpopulation of Ge-perturbed sites as compared to randomly occupied sites. This can be quantitatively interpreted in terms of an enthalpy difference of $\sim 60\mathrm{meV}$ between configurations with zero or one Ge in the first shell surrounding the impurity.

High-resolution Laplace deep-level transient spectroscopy spectra for gold- or platinum-diffused SiGe samples show an alloy splitting that is associated with the alloy fluctuations in the proximity of the defect. For the case of the platinum acceptor state, the effect of the level splitting caused by alloying in the first and also in the second shell of surrounding atoms can be distinguished. For the case of the gold acceptor, only the effect from the first shell of atoms is observable but the manifestation of alloying in the second-nearest shell can be seen as line broadening. We have found that the electronic energy level is affected by alloying in the first-nearest neighborhood by a factor of 2–3 more than by alloying in the second-nearest shell. The absolute values of the energy differences obtained from the Arrhenius plots for different defect configurations agree with those inferred from the peak separations observed in the spectra. A clear preference for gold and platinum to enter substitutional Si sites adjacent to Ge has been revealed. This may be interpreted in terms of an enthalpy lowering as a result of the fact that both metals are able to replace the host silicon atom more easily than the germanium atom in the substitutional position.