Michael K. Kelly

Large Free-Standing GaN Substrates by Hydride Vapor Phase Epitaxy and Laser-Induced Liftoff

Free-standing GaN, nearly equal in area to the original 2 inch wafer, was produced from 250–300 µm thick GaN films grown on sapphire by hydride vapor phase epitaxy (HVPE). The thick films were separated from the growth substrate by laser-induced liftoff, using a pulsed laser to thermally decompose a thin layer of GaN at the film-substrate interface. Sequentially scanned pulses were employed and the liftoff was performed at elevated temperature (>600°C) to relieve postgrowth bowing. After liftoff, the bow is only slight or absent in the resulting free GaN.

Optical patterning of GaN films

Patterned etching of GaN films was achieved with laser‐induced thermal decomposition. High‐energy laser pulses are used to locally heat the film above 900 °C, causing rapid nitrogen effusion. Excess gallium is then removed by conventional etching. At exposures of 0.4 J/cm2 with 355 nm light, etch rates of 50–70 nm per pulse were obtained. Illumination with an interference grating was used to produce trenches as narrow as 100 nm.

Lateral structuring of III‐V quantum well systems with pulsed‐laser‐induced transient thermal gratings

A two‐dimensional quantum well structure grown by molecular beam epitaxy has been laterally structured with an interference pattern from a high‐energy pulsed laser. The resulting thermal grating produces a reduction in the carrier density, which causes a lateral modulation in the band levels, with a period of 380 nm. Photoluminescence spectroscopy has been used for characterization.

Realization of AlGaAs antidot arrays by pulsed laser interference gratings

AlGaAs antidot arrays with about 107 antidots are produced by single-shot interference processing with a pulsed high-power Nd:YAG laser system. We apply magnetotransport experiments and atomic force microscopy (AFM) to explore the electronic and geometric properties of the arrays. The size of the antidot arrays are 3 mm×3 mm and the period varies from 400 to 1000 nm. The dots are elliptic or circular and have diameters ranging from 255 to 690 nm. The magnetotransport experiments are performed at 1.5 K in van der Pauw contact configuration. The laser structuring leaves the two dimensional electron density nearly unchanged but decreases the mobility by a factor of about 30. Several maxima are detected in the low magnetic field magnetoresistivity which are discussed based on the geometric data determined by AFM.