Using blue-emitting GaN/6H-SiC chips as primary light sources, we have fabricated green, yellow, red and white emitting LEDs. The generation of mixed colors, as turquoise and magenta is also demonstrated. The underlying physical principle is that of luminescence down- conversion (Stokes shift), as typical for organic luminescent dye molecules. A white emitting LED, using an inorganic converter, Y3Al5O12:Ce(3+)(4 integral of 1 ), has also been realized
The blue Mg induced 2.8 eV photoluminescence (PL) band in metalorganic chemical vapor deposition grown GaN has been studied in a large number of samples with varying Mg content. It emerges near a Mg concentration of 1x10(exp 19) cm(-3) and at higher concentrations dominates the room temperature PL spectrum. The excitation power dependence of the 2.8 eV band provides convincing evidence for its donor-acceptor (D-A) pair recombination character. It is suggested that the acceptor A is isolated Mg(Ga) while the spatially separated, deep donor (430 meV) D is attributed to a nearest-neighbor associate of a Mg(Ga) acceptor with a nitrogen vacancy, formed by self-compensation
The concentration p and the mobility mu of holes in metal-organic chemical vapor deposition (MOCVD) GaN:Mg layers were studied by room temperature Hall-effect measurements as a function of the Mg concentration N(A) in the range 3 x 10(exp 18) cm(exp-3) <= N(A) <= 1 x 10(exp 20) cm(exp -3). The hole density first increases with increasing N(A), reaches a maximum value p(max)~6*10(exp 17) cm(exp -3) at N(A)~2*10(exp 19) cm(exp - 3), decreases for larger N(A) values, and drops to very small values at N(A) 1 x 10(exp 20) cm(exp -3). The hole mobility decreases monotonically with increasing N(A) . The p(N(A)) data provide strong evidence for self-compensation, i.e., for a doping driven compensation of the Mg acceptor by intrinsic donor defects. This effect becomes significant when N(A) exceeds a value of 2 x 10(exp 19) cm(exp -3). A semiquantitative self-compensation model involving nitrogen vacancies is developed. It accounts satisfactorily for the measured p(N(A)) dependence and suggests that self-compensation limits the hole conductivity in bulklike MOCVD GaN:Mg layers grown near 1300 K to about 1.2 (omega cm)(exp -1))
We have studied band-gap renormalization and band filling in Si-doped GaN films with free-electron concentrations up to 1.7 x 10(exp19) cm(-3) , using temperature-dependent photoluminescence (PL) spectroscopy. The low-temperature (2 K) PL spectra showed a line-shape characteristic for momentum nonconserving band-to-band recombination. The energy downshift of the low-energy edge of the PL line with increasing electron concentration n, which is attributed to band-gap renormalization (BGR) effects, could be fitted by a n(1/3) power law with a BGR coefficient of - 4.7 X 10(exp-8) eV cm. The peak energy of the room-temperature band-to-band photoluminescence spectrum was found to decrease as the carrier concentration increases up to about 7 X 10(exp18) cm(-3) followed by a high-energy shift upon further increasing carrier concentration, due to the interplay between the BGR effects and band filling. The room-temperature PL linewidth showed a monotonic increase with carrier concentration, whic h could be described by a n(2/3) power-law dependence
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