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We present the concept and experimental realization of polarization-induced bulk electron doping in III-V nitride semiconductors. By exploiting the large polarization charges in the III-V nitrides, we are able to create wide slabs of high density mobile electrons without introducing shallow donors. Transport measurements reveal the superior properties of the polarization doped electron distributions than comparable shallow donor doped structures. The technique is readily employed for creating highly conductive layers in many device structures. PACS numbers: 61.72.Vv,72.20.-i, 73.40.-c Doping in semiconductors has been a much researched topic. The traditional shallow 'hydrogenic' doping technique is very well understood and gainfully employed. A good understanding of the role of ionized dopant atoms on carrier scattering in semiconductors led to the concept of modulation doping, which improved low temperature carrier mobilities in quantum-confined structures by many orders of magnitude [1]. The last decade witnessed the emergence of the III-V nitrides as a wide bandgap semiconductor with the property of large embedded electronic polarization fields owing to the lack of inversion symmetry in the crystal structure [2],[3]. This property has been widely exploited to make nominally undoped two-dimensional electron gases (2DEGs) in AlGaN/GaN heterostructures, which had led to high-electron mobility transistors (HEMTs) with record high performance characteristics[4]. The 2DEG at the AlGaN/GaN interface of a III-V nitride heterostructure is formed to screen the polar-

An overview is presented of progress in GaN electronic devices along with recent results from work at UCSB. From 1995 to 2001, the power performance of AlGaN/GaN high electron mobility transistors (HEMT) improved from 1.1 to 11 W mm-1, respectively. The disadvantage of the low thermal conductivity of the sapphire substrate was mitigated by flip-chip bonding onto AlN substrates, yielding large periphery devices with an output power of 7.6 W. A variety of HEMT amplifier circuits have been demonstrated. The first AlGaN/GaN heterojunction bipolar transistor (HBT) was demonstrated in 1998, with a current gain of about 3. By developing the technique of emitter regrowth, a current gain of 10 was achieved in both GaN BJTs and AlGaN/GaN HBTs. A common emitter current gain cutoff frequency of 2 GHz was measured. Critical issues involved in the growth of high quality AlGaN/(AlN)/GaN heterostructures and GaN:Mg by metal-organic chemical vapour deposition (MOCVD) and molecular beam epitaxy (MBE) and the device fabrication are discussed.

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The etch delay time commonly found during dry etching of AlGaN and GaN has been experimentally proven to be due to the presence of hard–to–etch surface oxides. A BCl3 deoxidizing plasma, followed by a Cl2 etching plasma, was found to give dead-time-free aluminum-mole-fraction-independent etch rates. No selectivity between GaN and AlGaN has been observed up to an aluminum mole fraction of 35%. The aluminum-mole-fraction-dependent etch rates commonly reported in literature have been related to the different dead-times associated with dissimilar surface oxides, disproving the more common explanations in terms of the higher binding energy of AlN compared to GaN and/or the lower volatility of AlClx compared to GaClx