A pn-heterojunction is fabricated by depositing an n-type β-Ga2O3 film by pulsed laser deposition (PLD) on c-cut Al2O3. P-type cuprous oxide films, Cu2O, are then deposited by PLD, as well as by radio frequency (RF) magnetron sputtering. It is concluded that hole injection is prohibited by a 3.26 eV valence band barrier, as measured by X-ray photo-electron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Heterojunction diode structures are prepared on the front side and electrical measurements demonstrate a rectification ration of 8 orders of magnitude and an ideality factor close to 2, indicating interface recombination-controlled forward current. The junction is also optically active and shows a very fast photo-response to 275 nm UV light. 

Pulsed laser ablation is used to form high-quality silicon-doped β-Ga2O3 films on sapphire by alternatively depositing Ga2O3 and Si from two separate sources. X-ray analysis reveals a single crystallinity with a full width at half maximum for the rocking curve around the (−201) reflection peak of 1.6°. Silicon doping concentration is determined by elastic recoil detection analysis (ERDA), and the best electrical performance is reached at a Si concentration of about 1 × 1020 cm−3, using optimized deposition parameters. It is found that a high crystalline quality and a mobility of about 2.9 cm2 (V s)−1 can be achieved by depositing Si and Ga2O3 from two separate sources. Two types of Schottky contacts are fabricated: one with a pure Pt and one with a PtOx composition. Electrical results from these structures are also presented. 

Secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) are utilized to study precipitation and the solubility of B in 4H-SiC epitaxial layers super saturated with B. Heat treatments are performed in Ar atmosphere in an rf-heated furnace at temperatures between 1700 and 2000 degrees C. SIMS ion images, and TEM micrographs reveal the formation of two types of precipitates where the larger, more thermally stable one is suggested to be B4C. The boron solubility is determined from SIMS depth profiles and is shown to follow the Arrhenius expression: 7.1 x 10(22) exp(-1.4 eV/k(B)T) cm(-3) over the studied temperature range.

The thermal stability of the passivating hydrogen-aluminum complex ((HAl)-H-2) in 4H-silicon carbide has been studied by determining the effective diffusion constant for hydrogen in an AI-doped epitaxial layer. Assuming a complex comprised of one H-2 and one AI acceptor ion, the extracted diffusivities provide the dissociation frequency of the complex. The extracted frequencies cover three orders of magnitude and yield a close to perfect fit to an Arrhenius equation with the extracted dissociation energy for the (HAl)-H-2-complex equal to 1.66 (+/-0.05) eV and a pre-exponential attempt frequency nu (0) = 1.7x10(13) s(-1) in good agreement with the expected value for a first order dissociation process.

We have applied scanning capacitance microscopy (SCM) to investigate SIC structures grown by vapour-phase epitaxy. The SCM technique is evaluated using n- and p-type doping staircase structures with doping concentrations ranging from 10(16) to 10(20) cm(-3). The n- and p-type doping was obtained by doping SiC with nitrogen and aluminium, respectively. The sample cross-sections for SCM were obtained by simple cleaving. For doping levels above 10(17) cm(-3) the SCM data are consistent with doping data obtained independently from secondary ion mass spectroscopy (SIMS). Treating the samples with diluted hydrofluoric acid significantly improves the SCM signal for the low-doped regions. The SCM technique has been used to investigate doping redistribution in patterned regrowth of n- and p-type SIC around dry-etched mesas. In both cases, contrast variations were seen close to the mesa walls, indicative of doping variations; lower and higher incorporation for p- and n-type, respectively. The observations are shown to be consistent with the expected trends in dopant incorporation in the SiC material.

The diffusion of deuterium (H-2) in epitaxial 4H-SiC layers with buried highly Al-acceptor doped regions has been studied by secondary ion mass spectrometry. H-2 was introduced in the near surface region by the use of 20-keV implantation after which the samples were thermally annealed. As a result, an anomalous accumulation of H-2 in the high doped layers was observed. To explain the accumulation kinetics, a model is proposed where positively charged H-2 ions are driven into the high doped layer and become trapped there by the strong electric field at the edges. This effect is important for other semiconductors as well, since hydrogen is a common impurity present at high concentrations in many semiconductors.

In this work we present for the first time, to our knowledge, the CVD epitaxial growth of β-SiC using an ion beam synthesized (IBS) β-SiC layer as seed, which has been formed by multiple implantation into Si wafers at 500 °C. The ion beam synthesized continuous layer is constituted by β-SiC nanocrystals that are well oriented relative to the silicon substrate. Comparison of the epitaxial growth on these samples with that on silicon test samples, both on and off-axis, is performed. The results show that the epitaxial growth can be achieved on the IBS samples without the need of the carbonization step and that the structural quality of the CVD layer is comparable to that obtained on a carbonized silicon sample. Improvement of the quality of the deposited layer is proposed.