N-polar GaN epitaxy and high electron mobility transistors

Abstract

This paper reviews the progress of N-polar (000 1) GaN high frequency electronics that aims at addressing the device scaling challenges faced by GaN high electron mobility transistors (HEMTs) for radio-frequency and mixed-signal applications. Device quality (Al, In, Ga)N materials for N-polar heterostructures are developed using molecular beam epitaxy and metalorganic chemical vapor deposition. The principles of polarization engineering for designing N-polar HEMT structures will be outlined. The performance, scaling behavior and challenges of microwave power devices as well as highly-scaled depletion-and enhancement-mode devices employing advanced technologies including self-aligned processes, n+ (In,Ga)N ohmic contact regrowth and high aspect ratio T-gates will be discussed. Recent research results on integrating N-polar GaN with Si for prospective novel applications will also be summarized.

Comparison of the Luminous Efficiencies of Ga- and N-PolarInxGa1−xN/InFernández-Garrido1, Lähnemann2, Hauswald3 et al. 2016Phys. Rev. Applied171140View full textAdd to dashboardCite

“…This value is comparable to the typical TD densities reported in the literature for GaN layers grown on 6H-SiC. 5,17 Quite unexpectedly, Fig. 6(c) also reveals the presence of a-type misfit dislocations (MDs) in sample I, well below the onset of significant plastic relaxation of the entire film in In x Ga 1−x N layers on GaN.…”

“…The other samples (G-J) contain nominally identical structures on 6H-SiC(0001), i. e., they are of opposite polarity. 5,16 The typical TD density of GaN layers grown by PA-MBE on 6H-SiC is on the order of 10 10 cm −2 . 5,17 The backside of the substrates was coated with Ti for efficient heat absorption during growth.…”

“…The first of these advantages is an enhanced In-incorporation efficiency. 5,6 This phenomenon is the result of the higher thermal stability of N-polar InN and paves the way for the use of signif- icantly higher substrate temperatures 7 that may help to improve the crystal quality as well as to minimize the incorporation of impurities. The second advantage is related to the expected improvement in device performance caused by the reversed direction of the polarization fields in the quantum wells (QWs) that constitute the active region of LEDs.…”

Stability diagrams for the surface patterns of GaN(0001¯) as a function of Schwoebel barrier height

“…The most intense investigations of crystal growth focus on in its Ga-polar (0001) orientation because it is easier to obtain stable process with smooth surfaces of this polarization. However growth at N-polar GaN(0001) surface focuses recently more and more attention because of wide variety of applications as solar cells, sensors, high electron mobility transistors and light emitting diodes [5][6][7]. There are reasons to believe that crystal grow in this polarization leads to structures of better quality.…”

Indium incorporation dynamics in N-polar InAlN thin films grown by plasma-assisted molecular beam epitaxy on freestanding GaN substrates

“…N-polar HEMTs also offer improved scalability through independent control of the gate-2DEG thickness and the barrier thickness, allowing the barrier design to compensate for the loss of sheet charge density as the channel thickness is scaled down [9]. In addition, the quantum displacement of the 2DEG towards the surface relative to the barrier/channel interface places the 2DEG closer to the gate, reducing short-channel effects and improving frequency performance [10]. In contrast to metal-polar grown InAlN, N-polar oriented indium-containing films have shown significantly higher indium incorporation for a given set of growth conditions [11][12][13][14][15], suggesting that the optimal growth conditions for N-polar InAlN may be significantly different than for metal-polar InAlN.…”