The role of extended and point defects, and key impurities such as C, O, and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation, and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes, and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

Gan : processing, defects, and devices

Record performance of high-power GaN/Al/sub 0.14/-Ga/sub 0.86/N high-electron mobility transistors (HEMTs) fabricated on semi-insulating (SI) 4H-SiC substrates is reported. Devices of 0.125-0.25 mm gate periphery show high CW power densities between 5.3 and 6.9 W/mm, with a typical power-added efficiency (PAE) of 35.4% and an associated gain of 9.2 dB at 10 GHz. High-electron mobility transistors with 1.5-mm gate widths (12/spl times/125 /spl mu/m), measured on-wafer, exhibit a total output power of 3.9 W CW (2.6 W/mm) at 10 GHz with a PAE of 29% and an associated gain of 10 dB at the -2 dB compression point. A 3-mm HEMT, packaged with a hybrid matching circuit, demonstrated 9.1 W CW at 7.4 GHz with a PAE of 29.6% and a gain of 7.1 dB. These data represent the highest power density, total power, and associated gain demonstrated for a III-nitride HEMT under RF drive.

High-power microwave GaN/AlGaN HEMTs on semi-insulating silicon carbide substrates

Biological materials naturally display an astonishing variety of sophisticated nanostructures that are difficult to obtain even with the most technologically advanced synthetic methodologies. As the needs for nanoengineered materials with improved performance characteristics are becoming increasingly important, the potential of biological scaffolds for the fabrication of novel types of nanostructures is being actively explored. This review presents an overview of “biotemplating” as an emerging, unique approach for the synthesis and organization of inorganic nanostructures into well-defined architectures. The technological significance of these architectures is emphasized. We review examples of biological templates explored to date (in terms of their origin and structure) and the success of a variety of methodologies in providing control over the size, crystallinity, and surface chemistry of the nanomaterials.

Biotemplated Nanostructured Materials

Nanocatalysis: size- and shape-dependent chemisorption and catalytic reactivity

We demonstrate well-controlled crystallographic etching of wurtzite GaN grown on c-plane sapphire using H3PO4, molten KOH, KOH dissolved in ethylene glycol, and NaOH dissolved in ethylene glycol between 90 and 180 °C, with etch rates as high as 3.2 μm/min. The crystallographic GaN etch planes are {0001}, {1010}, {101 1}, {101 2}, and {1013}. The vertical {1010} planes appear perfectly smooth when viewed with a field-effect scanning electron microscope. The activation energy is 21 kcal/mol, indicative of reaction-rate limited etching.

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Crystallographic wet chemical etching of gan

Low energy electron‐enhanced etching of Si(100) has been achieved by placing the sample on the anode of a dc discharge in hydrogen/helium mixtures. Over a broad range of gas composition, gas pressure, and discharge current, nonpatterned samples gave etch yields of 0.01–0.02 atoms/electron, and average etch rates of 2000–3000 A/min. Postetch examination by atomic force microscopy revealed surface roughness of 2–3 nm. These results are related to incident flux of H atoms and electrons through a simple model of the anode sheath layer above the sample.

Low energy electron‐enhanced etching of Si(100) in hydrogen/helium direct‐current plasma

Fabricating device structures from the III-N semiconductors requires dry-etching processes that leave smooth surfaces with stoichiometric composition after transferring patterns with vertical sidewalls. Results obtained by standard methods are summarized, and the extent of concomitant ion bombardment damage is assessed. A new low-damage technique—low-energy electron- enhanced etching—that avoids ion bombardment altogether is described, and early results for III-N materials are summarized. Etching issues critical in forming contacts and fabricating laser facets and mirrors are highlighted, and some prospects for future work are also identified.

The dry etching of group III-nitride wide-bandgap semiconductors

Low energy electron‐enhanced etching of GaAs(100) has been achieved by placing the sample on the anode of a low‐pressure hydrogen/chlorine dc discharge. Samples etched at room temperature reveal good anisotropy (≳20), good selectivity (≳200 against SiO2 masks at room temperature), and smooth surfaces at etch rates of 250 A/min; etch rates up to 4.5 μm/min were achieved at 150 °C. The dependence of the etch characteristics on gas composition, pressure, and temperature is described.

Low energy electron‐enhanced etching of GaAs(100) in a chlorine/hydrogen dc plasma

Hetero-epitaxial films of GaN(OOOl), deposited on SiC(OOOl) by organometallic vapor phase epitaxy and masked by 200 nm of SiO2, have been patterned by low energy electron enhanced etching (LE4) in hydrogen and chlorine dc plasmas at room temperature. Lines 2.0 µm wide showed highly anisotropic etching: straight side walls, no overcut, no trenching, and no “pedestal” at the base of the line. Root mean square (RMS) surface roughness of the films as grown was 8.5–10A; after LE4, RMS surface roughness of the etched surfaces was 2.5A.

D. A. Choutov

Papers

Low energy electron‐enhanced etching of Si(100) in hydrogen/helium direct‐current plasma

The dry etching of group III-nitride wide-bandgap semiconductors

Low energy electron‐enhanced etching of GaAs(100) in a chlorine/hydrogen dc plasma

Highly anisotropic, ultra-smooth patterning of GaN/SiC by low energy electron enhanced etching in DC plasma

Formation of ordered nanocluster arrays by self-assembly on nanopatterned Si(100) surfaces