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This chapter focuses on understanding and optimization of several key aspects of GaN device processing. For example, to activate ion-implanted dopants it is necessary to preserve the surface during the required high temperature anneal. A novel rapid thermal processing up to 1500°C, in conjunction with AlN encapsulation, is capable of activating high dose implants, although for most applications an anneal temperature of 1100–1150°C is sufficient to achieve reasonable activation. The activation processes of implanted Si or Group VI donors and common acceptors in GaN by using this ultrahigh temperature annealing, along with its effects on surface degradation, dopant redistribution and damage removal are discussed. 1400°C has proven to be the optimum temperature to achieve high activation efficiency and to repair the ion-induced lattice defects. Ion implantation can also be employed to create high resistivity GaN. Damage-related isolation with sheet resistances of 10 Ω/□ in n-GaN and 10 Ω/□ in p-GaN have been achieved by implanting O and transition metal elements. Effects of surface cleanliness on characteristics of GaN Schottky contacts have been investigated, and the reduction in barrier height was correlated with removing the native oxide that forms an insulating layer on the conventionally cleaned surface. W alloys have been deposited on Si-implanted samples and Mg-doped epilayers to achieve ohmic contacts with low resistance and better thermal stability than the existing non-refractory contact schemes. Dry etching damage in GaN has been studied systematically using Schottky diode measurements. Wet chemical etching and thermal annealing processes have been developed to restore the ion-degraded material properties.

In this chapter, the characteristics of dry etching of the AlGaInN materials system in different reactor types and plasma chemistries are reviewed, along with the depth and thermal stability of etch-induced damage. The application to device processing for both electronics and photonics is also discussed.

GaN power Schottky diodes have numerous advantages over more conventional Si rectifiers, achieving a maximum electric field breakdown strength over 10 times larger and on-state resistance R approximately 400 times lower at a given voltage. These characteristics have made GaN devices attractive for hybrid electric vehicles and power conditioning in large industrial motors. In particular, Schottky rectifiers are attractive because of their fast switching speed, which is important for improving the efficiency of inductive motor controllers and power supplies. Both GaN and SiC power Schottky diodes have demonstrated shorter turn-on delays than comparable Si devices. In this chapter we review the design and fabrication of GaN power rectifiers.

There is renewed emphasis on development of robust solid-state sensors capable of uncooled operation in harsh environments. The sensors should be capable of detecting chemical, gas, biological or radiation releases, as well as be able to send signals to central monitoring locations. In this chapter we discuss the advances in use of GaN-based solid-state sensors for these applications. AlGaN-GaN high electron-mobility transistors (HEMTs) show a strong dependence of source-drain current on the piezoelectric polarization-induced 2DEG. Furthermore, spontaneous and piezoelectric polarization-induced surface and interface charges can be used to develop very sensitive but robust sensors for the detection of gases, polar liquids and mechanical pressure. It has been demonstrated that AlGaN-GaN HEMT structures exhibit large changes in source-drain current upon exposing the gate region to various block co-polymer solutions. Pt-gated GaN Schottky diodes and ScO-AlGaN-GaN metal-oxide semiconductor diodes also show large change in forward currents upon exposure to H-containing ambients. Of particular interest are methods for detecting ethylene (CH), which offers problems because of its strong double bonds and hence the difficulty in dissociating it at modest temperatures. Apart from combustion gas sensing, the AlGaN-GaN heterostructure devices can be used as sensitive detectors of pressure changes. In addition, large changes in source-drain current of the AlGaN-GaN HEMT sensors can be detected upon adsorption of biological species on the semiconductor surface. Finally, the nitrides provide an ideal platform for fabrication of surface acoustic wave (SAW) devices. Given all these attributes, the GaN-based devices appear to be promising for a wide range of chemical, biological, combustion gas, polar liquid, strain and high temperature pressure-sensing applications. In addition, the sensors are compatible with high bit-rate wireless communication systems that facilitate their use in remote arrays.

The field of semiconductor spintronics seeks to exploit the spin of charge carriers in new generations of transistors, lasers and integrated magnetic sensors. There is strong potential for new classes of ultra-low power, high-speed memory, logic and photonic devices based on spintronics. The utility of such devices depends on the availability of materials with practical magnetic ordering temperatures, and most theories predict that the Curie temperature will be a strong function of bandgap. In this chapter we review the current state of the art in producing room-temperature ferromagnetism in GaN-based materials, the origins of the magnetism and its potential applications.

The use of gate insulators for compound semiconductor electronics would alleviate many of the problems encountered in current Schottky-based devices. Further, circuit design can be simplified, since enhancement-mode MOSFETs can be used to form single supply voltage control circuits for power transistors. The use of MOSFETs also allows the use of complementary devices, thus producing less power consumption and simpler circuit design. A critical need is to develop reliable methods for deposition of these insulating films. This will enable the development of a new class of compound semiconductor electronics for high-speed communication and data processing applications. Both MgO and ScO are shown to provide low interface state densities (in the 10 eV cm region) on n- and p-GaN, making them useful for gate dielectrics for MOS devices and also as surface passivation layers to mitigate current collapse in GaN-AlGaN HEMTs. Clear evidence of inversion has been demonstrated in gatecontrolled MOS p-GaN diodes using both types of oxide. Charge pumping measurements on diodes undergoing a high-temperature implant activation anneal show a total surface state density of ∼3 × 10 cm. On HEMT structures, both oxides provide effective passivation of surface states, and these devices show improved output power. The MgO-GaN structures are also found to be quite radiation resistant, making them attractive for satellite and terrestrial communication systems requiring a high tolerance to high-energy (40 MeV) protons.