Development Of Vertical Bulk Gallium Nitride Power Devices

Author : Saba Rajabi
Publisher :
ISBN 13 : 9781085572613
Total Pages : pages
Book Rating : 4.5/5 (726 download)

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Download or read book Design and Fabrication of Nitrogen Polar Gallium Nitride Vertical Transistors for High-power and High-frequency Applications written by Saba Rajabi and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Gallium nitride (GaN) has remarkable potential to extend the silicon-based semiconductor industry, which is currently plateauing in performance due to its materials limits Any significant improvement comes with a price that may not be a sustainable way to support the need for next generation electronic devices. With a more efficient semiconductor, such as a GaN, engineers could design and fabricate compact devices with ultra-high-scale density, because of GaN’s high electric field strength, saturation velocity, and electron mobility. Studies have already indicated that GaN device technology has tremendous potential for high-frequency communications and photonic applications. Because of advances in growth on commercially feasible large-area substrates, high radio frequency (RF) power applications of GaN are approaching commercialization. The basic material properties of GaN translate to smaller devices, which can lead to higher operation frequencies and lower switching losses. At the same time, the component count and size of passives has decreased. To date, most reported GaN-based field effect transistors have been in a Gallium polar (Ga-polar) orientation. Recent reports have suggested that Nitrogen polar (N-polar) GaN device technology is highly attractive for high RF power applications. The reverse polarization field in N-polar GaN compared to Ga-polar GaN promises unique design advantages. For example, an Al(Ga)N back barrier induces two-dimensional electron gas (2DEG) in the GaN channel and simultaneously confines electrons into the channel. Because of improved electron confinement in the channel and the higher aspect ratio, N-polar devices can presumably achieve superior performance. Additionally, N-polar devices offer lower specific contact resistance since the contacts to the 2DEG occur through GaN rather than wider-bandgap AlGaN material, which is necessary in Ga-polar devices. Previous results have clearly established that vertical devices in the form of current aperture vertical electron transistors (CAVETs) produce dispersion-less output current-voltage (IV) characteristics with a higher blocking electric field than that of lateral devices. The electric field being buried in the bulk of the material is helpful to achieve dispersion-less output characteristics compared to high electron mobility transistors (HEMTs), where surface states cause “knee walkout” or current collapse under high frequencies. Therefore, merging a N-polar high aspect ratio channel with a vertical drift region, as a CAVET does, is an attractive design to accomplish higher RF power performance compared to lateral counterparts. An integral part of a CAVET is the current blocking layer (CBL), which blocks the current flow from all paths except the aperture. Ga-polar CAVETs have been developed with either a Mg-doped GaN CBL or [Mg2+] ion-implanted GaN CBL. The latter is an attractive technique since it can alleviate regrowth in trenches. Notably, Mg ions diffuse out during the channel regrowth process at high temperatures. An AlN interlayer with a thickness of less than a nanometer is an effective solution to stop Mg ions from diffusing out into the channel layer and thereby causing uncontrollable threshold voltage shifts. It is crucial to mention that an AlN back barrier is an essential part of the structure of a vertical N-polar device design, as it is necessary to form the 2DEG channel as well as a diffusion barrier to arrest Mg out-diffusion. Thus, it renders N-polar vertical devices an especially appealing class of devices for RF application.This dissertation aims to provide a physical understanding and insight regarding the N-polar CAVET as well as the device’s design, performance and thermal analysis.