Substrates and epitaxial deposition processes for Group III-nitride thin films and power device heterostructures
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Introduction Power devices are key candidate electronic components for future reduction in global energy consumption. Power devices fabricated in wide-bandgap semiconductors are increasing their share of this market and are poised to play a significant role over a wide range of power requirements in applications now dominated by silicon devices and in areas where the latter devices cannot compete. An example of a power device structure for radio frequency (RF) and high-voltage applications is the AlGaN/GaN high-electron-mobility transistor (HEMT) (please see the review of the reliability of these and other GaN-based devices in the article by Hilt et al. in this issue). These devices possess a two-dimensional electron gas with a high carrier density and a very high saturated electron drift velocity, which allow high-saturated current densities, a reduction in transistor area, and high watts per unit gate periphery. They exhibit both low ON-resistance and high-blocking voltages and can operate in severe environments. The required processing conditions for these devices are possibly amenable for use in Si processing lines and co-integration with Si electronics on the same chip. These devices also have the potential for surpassing the limits of both Si and SiC power devices, as indicated by Baliga’s figure
of merit for power semiconductor devices operating in highfrequency circuits.1 Lateral AlGaN/GaN discrete RF power HEMTs fabricated on either sapphire or SiC substrates have been available as off-the-shelf devices for several years (see Reference 2). Within this time frame, extensive research and commercial development of thin film growth of chemically stable and electrically viable HEMT heterostructures on silicon substrates have been ongoing (please see article by Semond et al. in this issue). Commercial success of these latter devices operational up to 600 V for >106 h has been achieved. Devices operational up to 800 V have been demonstrated in the laboratory.3 GaN-based pure vertical Schottky diodes that are essentially an electronic junction between a metal and a semiconductor and lateral metal oxide semiconductor field-effect transistors (MOSFETs), wherein an oxide layer such as SiO2 separates a metal gate electrode from the current carrying channel of the semiconductor, and hybrid MOS-HEMT high-voltage power devices have also been extensively investigated. Depletion MOSFETs, in which the electrically conducting channel is normally ON and an applied voltage is required to turn it OFF, and enhancement-mode MOSFETs, in which the electrically conducting channel is normally OFF and an applied voltage is
Robert F. Davis, Carnegie Mellon University; [email protected] DOI: 10.1557/mrs.2015.92
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MRS BULLETIN • VOLUME 40 • MAY 2015 • www.mrs.org/bulletin
© 2015 Materials Research Society
SUBSTRATES AND DEPOSITION FOR GROUP III-NITRIDE FILMS AND DEVICES
required to turn it ON, fabricated on silicon substrates are now commercially available. At least one book on the subject has been published.4 However, the reliabili
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