No abstract

Spectroscopic ellipsometry was used to assess the preparation of smooth and abrupt GaN, AlN, and AlGaN surfaces by wet chemical treatments in real time. About 20–50 Å of overlayer typically can be removed from air-exposed samples.

AlN and GaN epitaxial heterojunctions on 6H-SiC(0001): Valence band offsets and polarization fields

We have investigated spectroscopically the gain characteristics of InGaN quantum well (QW) diode lasers. While the transparency condition can be reached at a moderate current density, the filling of localized band-edge states is a prerequisite for achieving lasing in this profoundly nonrandom alloy.

Monocrystalline GaN(0001) thin films have been grown at 950 ± C on hightemperature, ഠ100 nm thick, monocrystalline AlN(0001) buffer layers predeposited at 1100 ± C on a(6H)-SiC(0001) Si substrates via OMVPE in a cold-wall, vertical, pancake-style reactor. These films were free of low-angle grain boundaries and the associated oriented domain microstructure. The PL spectra of the GaN films deposited on both vicinal and on-axis substrates revealed strong bound excitonic emission with a FWHM value of 4 meV. The near band-edge emission from films on the vicinal substrates was shifted slightly to a lower energy, indicative of films containing residual tensile stresses. A peak attributed to free excitonic emission was also clearly observed in the on-axis spectrum. Undoped films were too resistive for accurate Hall-effect measurements. Controlled n-type, Si-doping in GaN was achieved for net carrier concentrations ranging from approximately 1 3 10 17 cm 23 to 1 3 10 20 cm 23 . Mg-doped, p-type GaN was achieved with n A -n D ഠ 3 3 10 17 cm 23 , r ഠ 7 V ? cm, and m ഠ 3 cm 2 ͞V ? s. Double-crystal x-ray rocking curve measurements for simultaneously deposited 1.4 mm GaN films revealed FWHM values of 58 and 151 arcsec for deposition on on-axis and off-axis 6H-SiC(0001) Si substrates, respectively. The corresponding FWHM values for the AlN buffer layers were approximately 200 and 400 arcsec, respectively.