Growth and characterization of plasma-assisted molecular beam epitaxial-grown AlGaN/GaN heterostructures on free-standing hydride vapor phase epitaxy GaN substrates
ABSTRACT 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.Electronics Letters 06/2006; · 1.04 Impact Factor
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ABSTRACT: The intensity of the flux of activated nitrogen from an RF inductively coupled discharge source for the plasma-assisted molecular beam epitaxy (PAMBE) of group III nitrides (A3N) can be linearly controlled using a modified output diaphragm design and increased nitrogen supply (∼5 sccm). This source provides a linear variation of the maximum A3N growth rate from 0.2 to 0.8 μm/h for the RF power controlled between 110 and 200 W, respectively. The use of excited nitrogen molecules favorably influences the growth of GaN and InN epilayers, which are characterized by a perfect structure and high optical quality.Technical Physics Letters 01/2007; 33(4):333-336. · 0.56 Impact Factor
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ABSTRACT: The authors have investigated the growth and structural and electrical properties of homoepitaxial GaN layers and GaN/AlGaN heterostructures grown on free-standing, hydride vapor phase epitaxy grown, N-polar GaN:Fe substrates by rf-plasma molecular beam epitaxy. Secondary-ion mass spectroscopic analysis of unintentionally doped and Be-doped N-polar GaN layers indicate that oxygen is the dominant impurity in all layers and is largely insensitive to growth temperature in the range investigated (675 °C < TS < 760 °C). Transmission electron microscopy (TEM) indicates that threading dislocations are generated at the regrowth interface in these samples; in contrast to homoepitaxial growth on Ga-polar GaN, and that the density of threading dislocations diminishes as the growth temperature increases. However, examination by TEM indicates that threading dislocations are not generated at the regrowth interface of samples subjected to pregrowth substrate surface cleaning by gallium deposition and desorption and subsequent growth of ultrathin (15 Å) initial AlN layers. N-polar GaN/AlGaN heterostructures grown on Be-doped homoepitaxial N-polar GaN buffers exhibit low buffer leakage and Hall mobilities up to 1680 cm2/Vs at sheet densities of 1.3 × 1013 cm-2. High electron mobility transistors have been fabricated on these structures; drain current densities over 700 mA/mm and breakdown voltages as high as 70 V have been measured.Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 01/2012; 30:02B113. · 1.36 Impact Factor