In As ∕ Al Sb high-electron-mobility transistors by molecular-beam epitaxy for low-power applications

Abstract

In As ∕ Al Sb high-electron-mobility transistor technology has transitioned from research to development stages in recent years. Development efforts at Northrop Grumman Space Technology, in collaboration with the Naval Research Laboratory and the University of California, Los Angeles, have focused on X-band and W-band low-noise amplifier monolithic millimeter-wave integrated circuits fabricated for applications requiring ultralow-power dissipation. The materials for the circuits discussed in this article were grown at Northrop Grumman Space Technology on 3-in.-diameter semi-insulating GaAs substrates by molecular-beam epitaxy. Atomic-force microscopy of the as-grown surface on each wafer showed that the rms roughness for all of the wafers ranged between 0.5 and 3.5nm, and this range of roughness was fully compatible with the fabrication process. The high electron mobility that InAs can provide was achieved reproducibly in these materials. It was maintained almost always above 25000cm2V−1s−1, and in several cases even exceeded 30000cm2V−1s−1. The associated electron sheet concentration ranged between 1.2×1012 and 1.8×1012cm−2. These combined mobilities and sheet concentrations gave corresponding sheet resistances in the range of 170±40Ω∕sq, with nonuniformity below 6% over these 3-in.-diameter wafers. These materials characteristics enabled successful fabrication of several recently published X-band and W-band low-noise amplifier circuits, and figures of merit for the circuits that were made specifically from these materials are referenced in this article.

AlGaSb Buffer Layers for Sb-Based Transistors

“…In previous work on InAs-channel HEMTs [with Al(Ga)Sb buffer thicknesses of 2.0 lm to 2.4 lm] we found that rms values of 0.5 nm to 3.5 nm were consistent with high mobilities and MMIC fabrication processes. 22,30 The ability to achieve smooth surfaces after relatively thin buffer layers of Al-rich AlGaSb on GaAs is consistent with our previous scanning tunneling microscopy images of 100-nm layers of AlSb on GaAs. 32 In our current work, we observed no obvious correlation between rms roughness and electron mobility, buffer layer growth rate, or buffer layer thickness over the ranges investigated.…”

“…It is not always clear why these higher values are sometimes achieved, but careful optimization of the arsenic flux may be important in some cases. 27,30,31 In this work, we did not attempt to optimize the arsenic flux. For growths 1 through 6, the 77-K mobilities ranged from 44,000 cm 2 /V s to 79,000 cm 2 /V s with no obvious correlation with buffer layer thickness or growth rate.…”

InAlSb/InAs/AlGaSb Quantum Well Heterostructures for High-Electron-Mobility Transistors

“…We have also grown structures using a 1.2-nm InAs(Si) doping layer 32,33 as well as InAlSb upper barriers, AlGaSb buffer layers, and small gate-to-channel separations (12 nm). Some samples also included a 20-nm n + InAs cap.…”

Antimonidation of ultrathin epitaxial aluminum nanofilms for metamorphic growth of Sb-based structures on GaAs substrates

“…These commonly seen methods for metamorphic device growth usually need the metamorphic buffer layers to be quite thick (around 1 μm) in order to accommodate defects and dislocations resulting from strain relaxation due to lattice mismatch. [17][18][19][20][21] Furthermore, low growth rates are used for the growth of metamorphic buffer layers in order to achieve good material quality. Therefore, growth of such thick metamorphic buffers takes time and greatly raises the production cost.…”