Red, green and blue (R-G-B) lasers and light emitting diodes are of interest
for applications in
high brightness, high definition displays. In these, the
ability to integrate the three colors onto
a single substrate is highly
desirable for easier fabrication and miniaturization of the devices.
Furthermore, semiconductor based white-light emitters could also be used as
light sources in
many applications. Much effort is currently being devoted to
the development of these devices,
for which group-III nitrides and wide bandgap
II-VI's have been the materials primarily explored.
During the past five years we have developed a family of II-VI wide bandgap
materials that
exhibit promising characteristics. ZnMgCdSe quantum well (QW)
structures grown
lattice-matched to InP substrates can emit light in the range
of 2.1 to 3.0 eV, overlapping
almost entirely with the visible spectrum range.
For emission in the red, a strained QW with
excess Cd can be used. Photopumped
lasers in the R-G-B have been demonstrated from these
structures, where only the
QW thickness or composition was varied. The growth conditions
by MBE have been
optimized so that defect densities are in the range of 10^4/cm^2. n-type
doping
in the 10^18/cm^3 range is possible for the quaternaries. p-type conductivity
can also
be achieved, although the levels are still somewhat low (~10^16/cm^3).
A lattice-matched
ZnSeTe layer (p~2 x 10^19/cm^3) has been developed for p+
ohmic contact formation.
Full-color LEDs have been fabricated and tested, and
injection lasers are under development.
To explore R-G-B integration, we have
used selective area epitaxy and have grown adjacent
patterned QWs on a single
substrate, which emit in the R-G-B regions. New directions include
the design of
a white-light LED that combines these three emitters in one.
Fig.1: Enjoying the banquet at the NAMBE Conference in Banff.
Fig.2: Conference organizers and friends at the NAMBE Conference Banquet, Banff.