Inside Back Cover (Phys. Status Solidi A 5/2010)

Abstract

The Feature Article by Morkoç and co‐workers () centers around the not so intuitive phenomena in two types of GaN based devices, namely InGaN based LEDs and InAlN barrier GaN heterojunction FETs. In terms of the LEDs, the paper uncovers that the quantum efficiency degradation observed at high current injection levels is not necessarily of Auger recombination origin. Furthermore, nearly similar behavior of LEDs on c‐plane and mplane suggests that the main driving force for the efficiency degradation is not polarization induced field either. The data along with their interpretation should set the stage for an accurate physics‐ based model to be developed. In terms of the FETs, the authors show that there is an optimum sheet density, which depends on drain bias or the electric field in the channel, at which the LO phonon lifetime is shortest, the velocity is highest, and the device degradation is least. The average optimum density is near 7 × 1012 cm−2 which challenges the proverbial notion that the higher the sheet density the better it is. Another outcome of this discussion is that heat dissipation takes the route of hot electrons giving off heat to LO phonons which in turn give it to LA phonons when they decay. Naturally, the shortest LO phonon lifetime is best for heat removal and thus the devices are more reliable in addition to electrons traversing at the highest velocity.

Record-low contact resistance for InAlN/AlN/GaN high electron mobility transistors on Si with non-gold metal

“…The observed of small I D collapse in the gate-lag measurement is due to the lattice-matched InAlN/AlN/GaN HEMT structure, thus the absence of piezoelectric polarization. The strain-free InAlN barrier layer has also been verified by Leach et al 30) . In addition, the surface-related current collapse is also suppressed by the optimized SiN passivation with (NH 4 ) 2 S x pretreatment 31,32) .…”

Stress test measurements of lattice‐matched InAlN/AlN/GaN HFET structures

“…The HFETs employed Ti/Al/Ni/Au Ohmic and Pt/Au Schottky contacts. Details of the growth procedure as well as the fabrication can be found in Ref 4.…”

“…GaN based heterostructure field effect transistors (HFETs) exhibit remarkable performance in the high frequency‐high power arena. Currently, research is focused on substitution of the AlGaN barrier with an In x Al 1− x N barrier 1–5. The reason is twofold.…”

“…The reason is twofold. First, InAlN can be grown lattice‐matched to the GaN although the exact composition for lattice matching is not precisely known due to the controversial values of the lattice parameters of InN, the bowing parameter of InAlN, and the strain state of the underlying GaN 4, 5. Nevertheless, the use of InAlN is important since the strain typically present in AlGaN‐based HFETs could be eliminated, which bodes well for reliability of the devices 6–8.…”

Piezotronic effect in AlGaN/AlN/GaN heterojunction nanowires used as a flexible strain sensor

“…Due to the non-centrosymmetric structure of the group-III nitride semiconductor materials (e.g., GaN, AlN, and AlGaN), spontaneous polarization ( P sp ) and piezoelectric polarization induced by lattice mismatch ( P lm ) are inevitably introduced during the epitaxial growth process [ 1 – 3 ]. Furthermore, the analysis of the internal polarization of the AlGaN/AlN/GaN heterojunction showed the existence of a 2D electron gas (2DEG), which effectively suppresses the degradation of the carrier mobility caused by the scattering at charge impurity centers [ 4 ].…”