A room-temperature photoelectrochemical etching process for n-type GaN films using a 0.04 M KOH solution and Hg arc lamp illumination is described. The process provides highly anisotropic etch profiles and high etch rates ͑Ͼ300 nm/min͒ at moderate light intensities ͑50 mW/cm 2 @365 nm͒. The etch rate and photocurrent are characterized as a function of light intensity for stirred and unstirred solutions, and the etch process is found to be diffusion limited for light intensities greater than 20 mW/cm 2 @365 nm. A reaction mechanism for the etch process is proposed.

Gallium nitride is used to fabricate high brightness blue and green light-emitting diodes in spite of high densities of extended structural defects. We describe a photoelectrochemical etching process that reveals the dislocation microstructure of n-type GaN films by selectively removing material between dislocations. The GaN whiskers formed by the etching have diameters between 10 and 50 nm and lengths of up to 1 μm. A correlation between the etched features and threading dislocations in the unetched film is confirmed through transmission electron microscopy studies. The whisker formation is believed to be indicative of electrical activity at dislocations in GaN.

Performance capabilities in traditional microelectronics are measured mainly in terms of speed, power efficiency, and level of integration. Progress in other, more recent, forms of electronics is driven instead by the ability to achieve integration on unconventional substrates (e.g., low-cost plastics, foils, paper) or to cover large areas. [1,2] For example, new forms of X-ray medical diagnosis might be achieved with large-area imagers that can conformally wrap around the body and digitally image the desired tissue.[3] Lightweight, wall-size displays or sensors that can be deployed onto a variety of surfaces and surface shapes might provide new technologies for architectural design. Various materials including small organic molecules, [4][5][6][7][8] polymers, [9] amorphous silicon, [10][11][12] polycrystalline silicon, [13][14][15][16] single crystalline silicon nanowires, [17,18] and microstructured ribbons [19][20][21][22] have been explored to serve as semiconductor channels for the type of thin-film electronics that might support these and other applications. These materials enable transistors with mobilities that span a wide range (from 10 -5 to 500 cm 2 V -1 s -1 ), and in mechanically bendable thin-film formats on flexible substrates. Applications with demanding high-speed operations, such as large-aperture interferometric synthetic aperture radar (InSAR) and radio frequency (RF) surveillance systems, require semiconductors with much higher mobilities, such as GaAs or InP. The fragility of single crystalline compound semiconductors creates a number of fabrication challenges that must be overcome in order to fabricate high-speed, flexible transistors with them. We recently established a practical approach to build metal semiconductor field-effect transistors (MESFETs) on plastic substrates by using printed GaAs wire arrays created from high-quality bulk wafers. [23,24] These devices exhibit excellent mechanical flexibility and unity current gain frequencies (f T ) that approach 2 GHz, even in moderately scaled devices (e.g., micrometer gate lengths). The work described in this article demonstrates GaAs ribbon based MESFETs (as opposed to our previously reported wire devices) designed with special geometries that provide not only bendability, but mechanical stretchability to levels of strain (strain ranges of > 20 %) that significantly exceed the intrinsic yield points of GaAs itself (ca. 2 %). The resulting type of stretchable, high-performance electronic systems can provide extremely high levels of bendability and the capacity to integrate conformally with curvilinear surfaces. The work that we report on this GaAs system extends our recently described "wavy" silicon [25] in four important ways: i) it demonstrates stretchability in GaAs, a material that is in practical terms much more mechanically fragile than Si; ii) it introduces a new "buckled" geometry that can be used for stretchability together with or independently of the previously described "wavy" configuration; iii) it achieves a new class of s...

Contacts consisting of various single layer metals to n-type GaN have been formed and characterized. The current-voltage characteristics were measured for 17 different metals (Sc, Hf, Zr, Ag, Al, V, Nb, Ti, Cr, W, Mo, Cu, Co, Au, Pd, Ni, and Pt) deposited on the same epitaxial growth layer. The barrier height, ideality factor, breakdown voltage, and effective Richardson coefficients were measured from those metals which exhibited strong rectifying behavior. The barrier heights for these metal contacts were measured using current-voltagetemperature and capacitance-voltage techniques. It was found that an increase in metal work function correlated with an increase in the barrier height. The surface state density of GaN was approximated to be very similar to CdS and almost a factor of ten less than GaAs.

A room-temperature photoelectrochemical wet etching process is described that produces smoothly etched GaN surfaces using KOH solution and Hg arc lamp illumination. Atomic force microscope measurements indicate a root-mean-square etched surface roughness of 1.5 nm, which compares favorably to the unetched surface roughness of approximately 0.3 nm. Etch rates of 50 nm/min were obtained using a KOH solution concentration of 0.02 M and an illumination intensity of 40 mW/cm2. It is shown that the smooth etching occurs under conditions of low KOH solution concentration and high light intensities, which result in a diffusion-limited etch process.