Polarity Control in Group-III Nitrides beyond Pragmatism

Abstract

Controlling the polarity of polar semiconductors on nonpolar substrates offers a wealth of device concepts in the form of heteropolar junctions. A key to realize such structures is an appropriate buffer-layer design that, in the past, has been developed by empiricism. GaN or ZnO on sapphire are prominent examples for that. Understanding the basic processes that mediate polarity, however, is still an unsolved problem. In this work, we study the structure of buffer layers for group-III nitrides on sapphire by transmission electron microscopy as an example. We show that it is the conversion of the sapphire surface into a rhombohedral aluminum-oxynitride layer that converts the initial N-polar surface to Al polarity. With the various Al x O y N z phases of the pseudobinary Al 2 O 3 -AlN system and their tolerance against intrinsic defects, typical for oxides, a smooth transition between the octahedrally coordinated Al in the sapphire and the tetrahedrally coordinated Al in AlN becomes feasible. Based on these results, we discuss the consequences for achieving either polarity and shed light on widely applied concepts in the field of group-III nitrides like nitridation and low-temperature buffer layers.

Persistent Photoconductivity, Nanoscale Topography, and Chemical Functionalization Can Collectively Influence the Behavior of PC12 Cells on Wide Bandgap Semiconductor Surfaces

“…The roughness characteristics of each area are noteworthy, Figure c. The roughness difference is related to the response of each particular polar domain region to the particular growth conditions . The Ga‐polar regions (circles) are smooth with rms values of 2.1 ± 0.6 nm.…”

Structure of Ultrathin Native Oxides on III–Nitride Surfaces

“…Further, the agreement extends to the bond angles, matching experiment and theory to within 0.5 • .Given the structure of the stable 2D oxides, there are a number of consequences. First, inversion domain boundaries are often found in thin film nitrides(24), and the observed oxides offer a mechanism for their creation. Notably, the oxides inherently reverse polarity through the transition from octahedral to tetrahedral bonding as discussed above.The inversion of polarity in the outer most layer of the oxide would seed N-polar nitride growth.…”

GaN-Based Light-Emitting Diodes with Graphene Buffers for Their Application to Large-Area Flexible Devices

“…Recently, it was reported that Ga-polar GaN grows on N-polar GaN substrates with the introduction of surface-oxidized AlN thin films [27]. Mohn et al have shown that formation of a rhombohedral AlON layer may be able to convert an N-polar surface to a metal-polar one [28]. In the present case of GaN on AlN/graphene, surface-oxidized AlN layers were formed before GaN growth by thermal oxidization in air at 200…”