Growth and characterization of plasma-assisted molecular beam epitaxial-grown AlGaN/GaN heterostructures on free-standing hydride vapor phase epitaxy GaN substrates

Arizona State University, Phoenix, Arizona, United States
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society (Impact Factor: 1.46). 06/2005; 23(3):1190 - 1193. DOI: 10.1116/1.1885013
Source: IEEE Xplore


We have grown AlGaN/GaN high electron mobility transistor (HEMT) structures by plasma-assisted molecular beam epitaxy on free-standing n -GaN substrates grown by hydride vapor phase epitaxy. Reflection high energy electron diffraction patterns of the as-loaded wafers exhibit narrow streaks which persist throughout the growth. Atomic force microscopy shows smooth AlGaN surfaces with root-mean-square roughness of 10 Å over a 20×20 μ m 2 area. High resolution x-ray diffractometry indicates that the AlGaN peak is ∼20 % narrower than for similar structures grown on SiC. Hall mobilities, electron sheet densities, and sheet resistances were measured on ten 60×60 μ m 2 Hall test patterns defined photolithographically across the surface of the 10×10 mm 2 sample. Buffer leakage measurements demonstrate that a Be:GaN layer effectively isolates the channel from the conductive substrate. Average sheet resistances and sheet densities were 380 Ω/ ◻ and 0.94×1013 cm -2 , respectively. These HEMT structures exhibit room-temperature Hall mobilities in excess of 1900 cm 2/ V s . In addition, devices on these structures exhibit excellent pinch-off, low gate leakage, and saturated drain current densities of almost 700 mA/mm. Further details regarding the structural and electrical properties will be described along with device testing.

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    ABSTRACT: AlGaN/GaN high electron mobility transistors (HEMTs) by plasma-assisted molecular beam epitaxy on free-standing GaN substrates grown by hydride vapour phase epitaxy (HVPE) have been fabricated. Hall measurements yielded typical electron mobilities of 1750 cm<sup>2</sup>/Vs with sheet densities of 1.1×10<sup>13</sup> cm<sup>-2</sup>. Off-state breakdown voltages as high as 200 V were measured on unpassivated devices. Output power density at 4 GHz was measured to be 5.1 W/mm at a power-added efficiency of 46% and an associated gain of 13.4 dB. This constitutes significant improvement of RF performance by MBE-grown AlGaN/GaN HEMTs on free-standing HVPE GaN.
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