Palo Alto Research Center (PARC)
and Crystal IS demonstrate the first UV-LED on AlN substrates
April 2002
Palo Alto Research Center (PARC) and Crystal
IS announce the first demonstration of an optoelectronic device
grown on a single crystal substrate of AlN. The device, an ultra
violet light emitting diode (UV LED), was recently demonstrated
at PARC utilizing substrates produced by Crystal IS. Single crystal
AlN substrates present an excellent template for the growth of AlGaN
alloys, because of their chemical compatibility, well-matched crystal
structure and thermal expansion coefficients. An important application
of solid-state UV optical sources is anticipated to be compact and
highly sensitive bioagent detection systems for airborne pathogens
like Anthrax spores. Other potential applications of UV LEDs include
solid-state white lighting, sterilization and disinfectant devices,
and compact analytical devices for the biotechnology and pharmaceutical
markets.
UV-LED emission spectra measured at different drive currents.
The UV-LED was grown on a single crystal (0-112) AlN substrate
with a Si-doped graded AlGaN transition layer.
These are atomic force microscopy images of an (10-11) AlN
substrate before and after AlN homoepitaxy. The initial RMS
roughness in a 1-mm square prior to epitaxy was 0.83 nm and
this value decreased to 0.38 nm after AlN epitaxy.
The LED structure consisted of a GaN/AlGaN multiple-quantum-well
active region with emission wavelength near 360 nm. The LED devices
were 100 mm in diameter with a top p-electrode and a lateral n-contact.
The light was extracted through the transparent AlN substrate. Crystal
IS has started supplying research quantities of high-quality AlN
substrates and has demonstrated dislocations densities of less than
1000 cm-2. AlN substrates offer a very high thermal conductivity
(~320 W/m-K), which is important for high power operation of light
emitting devices. They also provide good lattice matching particularly
for AlGaN active regions with high Al concentrations as required
for deep-UV LEDs with emission wavelengths below 300 nm. Non-polar
substrate orientations are also available which may allow improvements
in the quantum efficiency of nitride-semiconductor LED’s and
laser diodes.
