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.

Semi‐insulating freestanding GaN substrates were produced by hydride vapor phase epitaxy using intentionally introduced iron impurity atoms to compensate residual donors in GaN. Variable temperature resistivity measurements determined the resistivity of an iron‐doped GaN sample to be ∼3 × 105 Ω cm at 250 °C. The activation energy of the carrier was 0.51 eV and room temperature resistivity was determined to be ∼2 × 109 Ω cm at room temperature by linear fitting and extrapolation to room temperature. Near‐infrared photoluminescence at 1.6 K exhibited sharp emission at 1.3 eV, associated with the 4T1(G) →6A1(S) internal transition of the Fe3+ charge state. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We fabricated high standoff voltage ͑450 V͒ Schottky rectifiers on hydride vapor phase epitaxy grown GaN on sapphire substrate. Several Schottky device geometries were investigated, including lateral geometry with rectangular and circular contacts, mesa devices, and Schottky metal field plate overlapping a SiO 2 layer. The best devices were characterized by an ON-state voltage of 4.2 V at a current density of 100 A/cm 2 and a saturation current density of 10 Ϫ5 A/cm 2 at a reverse bias of 100 V. From the measured breakdown voltage we estimated the critical field for electric breakdown in GaN to be (2.2Ϯ0.7)ϫ10 6 V/cm. This value for the critical field is a lower limit since most of the devices exhibited abrupt and premature breakdown associated with corner and edge effects. © 1999 American Institute of Physics. ͓S0003-6951͑99͒02409-2͔Wide band gap materials, primarily SiC and GaN, have recently attracted a lot of interest for applications in high power and high temperature electronics. Although the processing technology for SiC is more mature, GaN offers several advantages. First, there are various device possibilities using GaN/AlGaN heterojunctions which are not available in the SiC system. Second, the availability of cheap and efficient hydride vapor phase epitaxy ͑HVPE͒ growth technology achieving growth rates in excess of 100 m/h, have produced thick, high quality GaN layers on sapphire. 1 Third, by using AlGaN layers, one can take advantage of a larger band gap to achieve higher critical electric fields than in GaN alone.In this study, we focus on the fabrication of high voltage, GaN based Schottky rectifiers and the measurement of the critical field for electric breakdown. The critical field for electric breakdown is one of the most significant parameters in the design and performance of high power devices. It directly influences the required thickness of the standoff region in the Schottky rectifier and bipolar devices, such as the thyristor. Since the thickness of the standoff region sets the resistivity of the device, it will determine power dissipation and maximum current density of the device. 2,3 In previous studies, Schottky diodes have been fabricated on GaN using a variety of elemental metals including Pd and Pt, 4,5 , Au, Cr, and Ni,6,7 , and Mo and W. 8 More details on the metal-GaN contact technology can be found in Ref. 9.In this work, Schottky rectifiers were fabricated on 8-10 m thick GaN layers grown by HVPE on sapphire, where the electron concentration changes with the distance from the GaN/sapphire interface. We carried out conductivity and Hall measurements on a series of HVPE GaN films of varying thickness ranging from 0.07 to 9.2 m, and fitted the data to a two layer model. [10][11][12][13] From the model, we concluded that the GaN films consisted of a low conductivity, low electron concentration, 8-10 m thick top layer on a very thin (Ͻ100 nm), highly conductive, high electron concentration bottom layer. The electron concentrations and mobilities in the thin interface layer and thic...

The optical properties of n-type GaN grown by hydride vapor phase epitaxy, with intentional Si doping levels ranging from nominally undoped to ND−NA=4×1017 cm−3, are investigated using low temperature photoluminescence. We identify free and neutral donor-bound exciton transitions and two-electron satellites (TES) at 1.7 K. The energy difference between the principal neutral donor-bound exciton peak and its TES yields a Si donor binding energy of 22 meV. The intensity of the Si-related TES increases with increasing Si concentration. The Si donor is much shallower than the two residual donors, which have binding energies of 28 and 34 meV. This result suggests that the main residual donors in this material (and possibly in many layers grown by metal organic chemical vapor deposition and metal organic molecular beam epitaxy as well) are not Si. Silicon doping also introduces an acceptor level with a binding energy of about 224 meV.

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