An efficient carrier compensation mechanism in semiconductor layers by Fermi-level engineering is demonstrated using the modulation-doping of a deep acceptor and a shallow donor. The punch-through of the depletion region across the whole stack of modulation-doped layers shifts the Fermi level closer toward the midgap position, resulting in the compensation of residual background free carriers. The method represents an alternative to achieve semi-insulating properties in semiconductor materials where a suitable deep acceptor or donor state at the midgap position is not available. We demonstrate the applicability of the concept with a commercially important GaN case study using carbon (deep acceptor) and Si (shallow donor) doping. A strong enhancement of breakdown field strength and reduced charge pileup effects are observed due to the efficient pinning of the Fermi level.

Sputter epitaxy is a low-cost process suited for the deposition of group-III-nitride semiconductors and allowing the deposition on large substrate areas at lower growth temperatures than in metal-organic vapor phase epitaxy (MOVPE). High-quality AlN, AlGaN, and GaN epitaxially grown on Si(111) substrates by reactive magnetron sputtering are demonstrated and details on process parameters are given. With an ammonia-based reactive sputtering process in a high-purity environment, AlN can be grown with high crystalline quality comparable to the best MOVPE-grown samples regarding twist and tilt and with a very low surface roughness, free of the typical columnar structure of sputtered AlN and pits. Also AlGaN, typically required for strain engineering of GaN layers grown on Si, can be grown in the entire compositional range by co-sputtering of Al and Ga. Thin undoped buffer layer samples show high breakdown field strengths well above 2.5 x 10(6) V cm(-1) and demonstrate the possible use for field effect transistor (FET) buffer layers.

Sputtering epitaxy is a low cost process allowing large area deposition at lower growth temperatures than metalorganic vapour phase epitaxy (MOVPE) and may ease e.g. integration with Si CMOS technology. We present high quality AlN and GaN epitaxial layer structures grown on Si(111) substrates by reactive magnetron sputtering. By optimizing nucleation and growth on Si(111) substrates AlN layers are obtained with twist and tilt values comparable to MOVPE grown samples and with very low surface roughness free of any columnar structure. Also the entire compositional range of AlGaN has been addressed by co-sputtering of Al and Ga. Thin undoped buffer layer samples show high breakdown field strengths well above 1×10 6 V/cm which is prerequisite for FET applications. We also report on reactive sputtering of material combinations that are largely inaccessible to MOVPE, e.g., transition metal nitrides and AlScN.

•Epitaxial growth of AlN on Si (111) by pulsed reactive sputtering.•Change of N-precursor change growth mode from three-dimensionel to two-dimensional.•Change in growth mode approved by scanning transmission electron microscopy images.•Increase of ad-atom mobililty by use of NH3.•Smooth surface morphology for growth with NH3 with low roughness as 0.14 nm.

We present a pulsed reactive magnetron sputter process for high quality AlN on Si (111) beneficially avoiding any high-temperature growth. Initially, metallic aluminium with a nominal thickness of about one monolayer is deposited at a substrate temperature around 850 degrees C in an Ar plasma followed by sputtering in an Ar/N plasma. For 250 nm thick AlN layers a surface roughness below 0.2 nm rms is obtained as determined by atomic force microscopy (AFM). Using an Al nucleation step prior to AlN growth substantially improves the crystalline properties of AlN. The FWHM values of the AlN (0 0 0 2) and the AlN (1 0 1 0) diffraction peaks with 0.45 degrees and 0.86 degrees, respectively, are comparable to state-of-the-art AlN on Si layers grown by metalorganic vapour phase epitaxy (MOVPE). Two different N-precursor gases, namely N2 and NH3, lead to distinct layer qualities as revealed by atomic force microscopy and transmission electron microscopy. Only with NH3 substantial lateral growth can be achieved at T = 850 degrees C which is mandatory to obtain smooth surface morphologies. In MOVPE such lateral AlN growth is typically only achieved at high growth temperatures (T > 1000 degrees C).