The wide-ranging impact of III-Nitride semiconductors is well
known, encompassing high-brightness UV/blue/green/amber LEDs, UV/blue diode
lasers and high-power microwave transistors (>11 W/mm). Alongside these
impressive devices remain a surprising number of fundamental questions
regarding the material properties of III-N structures. This cluster of
articles addresses a variety of topics of current importance for the
understanding and application of the III-Nitrides, mostly originating from
groups within the UK.
Research into III-N materials and devices is widespread within the UK and
has the UK nitrides consortium (UKNC) as its premier forum
(http://www.uknitrides.org). From its origin in 1994, and with support from
the DTI/EPSRC from 1998 to 2001, the UKNC has grown rapidly with membership
now exceeding 40 separate groups with a healthy mix of academic and
industrial institutions. The second UKNC conference was held at Strathclyde
University in September 2001 with a programme including excellent invited
presentations from Nicolas Grandjean (CHREA-CNRS, Valbonne) and Oliver
Brandt (Paul Drude Institut, Berlin). The `flagship' paper of this cluster
is a manuscript submitted from the second of these, addressing the highly
important issue of the determination of the strain and composition within
InGaN structures. This paper gives an authoritative, novel and insightful
description of both the strengths and limitations of high-resolution x-ray
diffraction when applied to InGaN quantum well structures.
Within the UK a widespread infrastructure for the growth of III-Nitride
structures has developed including MOCVD reactors at Qinetiq Ltd, and the
Universities of Strathclyde, Bath, Sheffield and Cambridge and MBE/CBE
reactors at Sharp Laboratories of Europe and the Universities of
Nottingham, Cardiff and Liverpool. The MOCVD teams feature in this cluster
through papers from Strathclyde and Sheffield. The light-emitting
properties of InGaN quantum wells are probed using series of samples
emitting over the entire visible spectrum, by control of the growth
temperature of the well, and with variations in optical properties induced
by control of the growth temperature of the barrier. A second Sheffield
paper changes the focus to the electronic applications of AlGaN/GaN
structures, looking at surface passivation effects in transistors. The
other main growth technique is represented in the paper by Huang et al
discussing CBE of GaN bringing in the important dimension of substrate
choice, in this case silicon (111). Such factors also feature in the paper
from Oxford University describing deposition and in situ investigation of
novel InN structures. The large body of UK-based research into III-nitrides
not directly associated with material growth is exemplified by papers
within this cluster applying the powerful technique of muon spin resonance
to hydrogen in III-nitrides, analysing novel phonon replica structure in
sub-band gap absorption and calculations of the heterostructure band
offsets.
I am sure that within this selection of papers you will find interesting
insights into the remarkable world of III-Nitride physics and applications.
Dr Robert Martin, Guest Editor
April 2002