White light emitting diodes (LEDs) have been successfully fabricated for the first time in silicon carbide
substrates (4H-SiC) using a novel laser doping technique. The donor-acceptor pair (DAP) recombination mechanism for
luminescence has been used to tailor these LEDs. Chromium (Cr), which produces multiple acceptor sites per atom, and
selenium which produces multiple donor sites per atom were successfully incorporated into SiC for the first time using
laser doping. Aluminum (Al) and nitrogen (N) were also laser-doped into SiC. Green (521-575 nm) and blue (460-498
nm) wavelengths were observed due to radiative recombination transitions between donor-acceptors pairs of N-Cr and
N-Al respectively, while a prominent violet (408 nm) wavelength was observed due to transitions from the nitrogen level
to the valence band level. The red (698-738 nm) luminescence was mainly due to nitrogen excitons and other defect
levels. This RGB combination produced a broadband white light spectrum extending from 380 to 900 nm. The color
space tri-stimulus values were X = 0.3322, Y = 0.3320 and Z = 0.3358 as per 1931 CIE (International Commission on
Illumination) for 4H-SiC corresponding to a color rendering index of 96.56; the color temperature of 5510 K is very
close to average daylight (5500 K).
A direct-write pulsed Nd:yttrium-aluminum-garnet laser treatment in an aluminum-containing gas was applied to the polished surface of an undoped Ge wafer. After KOH etching to remove metallic aluminum deposited on the surface, secondary ion mass spectroscopy (SIMS) revealed ~60-200 nm penetration for Al at a concentration of ~1017 cm-3. Atomic force microscopy showed that surface roughness is much less than the measured penetration depth. Laser doping of Ge is a potential low cost, selective-area, and compact method, compared with ion-implantation, for production of high current ohmic contacts in Ge and SiGe opto-electronic devices.