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

We develop a reciprocal-space model that describes the (hkl) dependence of the broadened Bragg peakwidths produced by x-ray diffraction from a dislocated epilayer. We compare the model to experiments and find that it accurately describes the peakwidths of 16 different Bragg reflections in the [010] zone of both GaN and AlN heterolayers. Using lattice-distortion parameters determined by fitting the model to selected reflections, we estimate threading-dislocation densities for seven different GaN and AlGaN samples and find improved agreement with transmission electron microscopy measurements.

The interaction between cavity modes and optical transitions leads to new coupled light-matter states in which the energy is periodically exchanged between the matter states and the optical mode. Here we present experimental evidence of optical strong coupling between modes of individual sub-wavelength metamaterial nanocavities and engineered optical transitions in semiconductor heterostructures. We show that this behaviour is generic by extending the results from the mid-infrared (~10 μm) to the near-infrared (~1.5 μm). Using mid-infrared structures, we demonstrate that the light-matter coupling occurs at the single resonator level and with extremely small interaction volumes. We calculate a mode volume of 4.9 × 10−4 (λ/n)3 from which we infer that only ~2,400 electrons per resonator participate in this energy exchange process.

QzqiTime-resolved photolttminescence spectroscopy has been used to investigate carrier decay dynamics~t ifl> in a InXGa, -XASI.-,,NV (x-O.03, y -0.01) epilayer grown on GaAs by metal organic chemical vapor deposition. Time-resolved photohrmineseence (PL) measurements, performed for various 4%L excitation intensities and sample temperatures, indicate that the broad PL emission at low -gm temperature is dominated by localized exciton recombination. Lifetimes in the range of 0.07-0.34 a ns are measured; these photo luminescence iifetimes are significantly shorter than corresponding values obtained for GaAs. In particular, we observe an emission energy dependence of ,the decay lifetime at 10 K, whereby the Iifetime decreases with increasing emission energy across the PL spectrum. This behavior is characteristic of a distribution of localized states, which arises from alloy fluctuations. @ 2000 American institute of l&ecentIy, the quatemary InGaAsN alloy system has attracted a great deal of attention due to its potential application in devices such as next generation multifunction solar cells and optoelectronic devices for optical I-7 The alloy is of fundamental and technocommunications. logical interest because it exhibits an extremely large band gap bowing coefficient (b --14eV) between the HI-N and HI-As bhanes.x The extremely large bowing coefficient permits the InXGal _XAsl _YNYquaternary alloy to maintain lattice match to GaAs, with a wide range of tunable band gap energies smaller than the GSAS band gap for x-3y. Studies of InGaAsN solar cell structures with 1 eV band gap have shown that the quatemary suffers from a short minority carrier diffusion length.z3 More recent work has found that significantly improved minority hole diffusion-lengths may be obtained by thermally annealing the InGaAsN after growth, although minority electron diffusion lengths remain short.' In this letter, we report the results of time-resolved PL spectroscopy studies of an InGaAsN epilayer. Tfds letter is one of the first investigations of the carrier dynamics witfdn InGaAsN.A 3-pm-thick, htGaAsN epilayer was grown at a growth temperature of 590 "C by metal organic chemicaI vapor deposition on a semi-insulating GSAS substrate and terminated with a 5 nm GaAs calp.Trimethylindium, trimethylgallium, arsine, and dimethy:lhydrazine were used as source gases. The nominal In and N molar fractions were 0.03 and 0.01, respectively. The Irr/N incorporation ratio of three has been shown to provide lattice match to GaAs!'9 As grown, the unintentionally doped lhtGaAsN film was p type. After growth, the sample was annealed at 600 "C for 30 min in a nitrogen ambient in order to improve the electrical and optic al properties of the material. 1 Photohtminescence (PL) measurements for various sample temperatures and excitation intensities were performed with the sample mounted on a cold -a)Et&~~i~rnaikjiimg@physksmed" finger and cooled by a closed-cycle helium refrigerator. The sample was optically pumped with 580 nm laser pulses of 10 ps width and ...

To examine further the strain relaxation produced by inclined threading dislocations in AlGaN, a heterostructure with three AlGaN layers having successively increasing Ga contents and compressive strains was grown on an AlN template layer by metalorganic vapor-phase epitaxy. The strain state of the layers was determined by x-ray diffraction (XRD) and the dislocation microstructure was characterized with transmission electron microscopy (TEM). As the GaN mole fraction of the heterostructure increased from 0.15 to 0.48, the increased epitaxial strain produced inclined dislocations with successively greater bend angles. Using the observed bend angles, which ranged from 6.7° to 17.8°, the measured strain relaxation within each layer was modeled and found to be accounted for by threading-dislocation densities of 6–7×109/cm2, in reasonable agreement with densities determined by TEM and XRD. In addition to the influence of lattice-mismatch strain on the average bend angle, we found evidence that local strain inhomogeneities due to neighboring dislocations influence the specific bend angles of individual dislocations. This interaction with local strain fields may contribute to the large spread in the bend angles observed within each layer. A detailed TEM examination found that the initial bending of threading dislocations away from vertical often occurs at positions within <15 nm of the AlGaN/AlN heterointerface. Under the assumption that dislocation climb mediated by bulk-defect diffusion is effectively suppressed at the growth temperature, this result implies that inclination is established by processes occurring at the dynamic growth surface. We describe a mechanism where dislocation bending occurs by means of dislocation-line jogs created when surface steps overgrow vacancies that attach to threading-dislocation cores at their intersection with the growth surface.