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The design, growth by metal-organic chemical vapor deposition, and processing of an Ino,07G~~93As0~98N0~02 solar cell, with 1 .O eV bandgap, lattice matched to GaAs is described. The hole diffusion length in annealed, n-type InGaAsN is 0.6-0.8 p, and solar cell internal quantum efficiencies > 70% are obtained. Optical studies indicate that defects or impurities, from InGaAsN doping and nitrogen incorporation, limit solar cell performance.Multi-junction tandem solar cells are being developed as power sources for satellite systems operating in air mass zero (AMO) solar radiation. Models indicate that record efficiencies (= 38%) would be obtained for tandem cells where a 1.0 eV bandgap cell is added in series to proven InGaP-GaAs tandem structures.' The In,Ga,~,As,.,N, alloy system appears ideal for this application. Bandgaps of 5 1.0 eV are obtained for In,Ga,~,As,.,N, with minimal N concentrations ( y > 0.02), and the quaternary is latticematched to GaAs for compositions with x = 3y. '' Even at these low concenuations, N incorporation has proven problematic, and it remains a challenge to demonsuate thick (2-3 pm), high quality, In,Ga,.,As,.,N, (y > 0.02) epilayers needed for solar cell development. In this paper, we present a status report on In,Ga,~,As,.,N, properties, growth, and solar cell performance. , Under specialized conditions, we demonstate internal quantum efficiencies >70 9 ' 0 for I . O eV bandgap solar cells.The structures in this work were grown in a vertical flow, high speed rotaling disk, Emcore GS/3200 metalorganic chemical vapor deposition (MOCVD) reactor.In,Ga,-,As,,N, films were grown using trimethylindium (TMIn). lriniethylgallium (TMG), 100% arsine and dimethylhydrazine (DMf-Iy). Dirnetfiylhydrazine wits used x the nitrogen source since it has a lower disassociation temperature than ammonia and has a vapor pressurc or approximately 1 10 torr at 18°C. A significant increase in photoluminescence intensity was observed from these films following a post-growth anneaL4 Ex-situ, post -growth anneals were carried out in a rapid thermal anneal system under nitrogen using a sacrificial GaAs wafer in close proximity to the InGaAsN sample. The photoluminescence intensity was a maximum for samples annealed for either 700OC for 2 minutes or 65OOC for 30 minutes. Secondary ion mass spectrometry measurements showed the residual carbon concentration of similar films to be 6 -8~1 0 '~ cm". Carbon is incorporated during growth at sufficiently high levels to possibly cause the background p-type conductivity and the observed ex-situ annealing behavior.The optical properties of the InGaAsN films were extremely sensitive to N content, ex-situ annealing, and doping. Photoluminescence and optical absorption

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Ultraviolet light emitting diodes (LEDs) have been grown using metalorganic vapor phase epitaxy, while monitoring the 550 nm reflected light intensity. During nucleation of GaN on sapphire, the transition from three-dimensional (3D) grain growth to two-dimensional (2D) coalesced growth was intentionally delayed in time by lowering the NH3 flow during the initial high temperature growth. Initially, when the reflectance signal is near zero, the GaN film is rough and composed of partly coalesced 3D grains. Eventually, the reflected light intensity recovers as the 2D morphology evolves. For 380 nm LEDs grown on 3D nucleation layers, we observe increased light output. For LEDs fabricated on GaN films with a longer recovery time an output power of 1.3 mW at 20 mA current was achieved.

Ultraviolet light-emitting diodes (LEDs) have been grown by metalorganic vapor phase epitaxy using AlN nucleation layers and thick n-type Al0.48Ga0.52N current spreading layers. The active region is composed of three Al0.36Ga0.64N quantum wells with Al0.48Ga0.52N barriers for emission at 290 nm. Devices were designed as bottom emitters and flip-chip bonded to thermally conductive submounts using an interdigitated contact geometry. The ratio of quantum well emission to 330 nm sub-band gap emission is as high as 125:1 for these LEDs. Output power as high as 1.34 mW at 300 mA under direct current operation has been demonstrated with a forward voltage of 9.4 V. A peak external quantum efficiency of 0.18% has been measured at an operating current of 55 mA.