GaP Substrates Research Articles

Plasmonic Band Gap: Role of the Slit Width in 1D Metallic Grating on Higher Refractive Index Substrate

This paper reports the excitation of surface plasmon polaritons (SPPs) and associated plasmonic band gap (PBG) while using TM plane wave interacting with 1D metallic grating on higher refractive index GaP substrate. A simple method is introduced to estimate the PBG which is crucial for many plasmonic devices. The PBG is estimated by measuring the transmission spectra obtained through the plasmonic grating structures when slit width is varied while periodicity and the thickness of the gold (Au) film remained fixed. The PBG is observed for the grating devices whose slit width is less than one third of the periodicity which is caused by the presence of a higher plasmonic mode. The PBG is absent for the grating device whose slit width is slightly less than half and greater than one third of the periodicity. Such grating devices support only a fundamental plasmonic mode because the profile/shape of the slit in the grating device is more like a sinusoidal nature. Furthermore, such grating offers intermediate scattering to the incident light and the SPP as well which in turn couple more incident energy to the SPPs. Far-field modelling results also support the results obtained through experiment.

Enhanced conversion efficiency in wide-bandgap GaNP solar cells

In this work, we demonstrate ∼2.05 eV dilute nitride GaNP solar cells on GaP substrates for potential use as the top junction in dual-junction integrated cells on Si. By adding a small amount of N into indirect-bandgap GaP, GaNP has several extremely important attributes: a direct-bandgap that is also tunable, and easily attained lattice-match with Si. Our best GaNP solar cell ([N] ∼ 1.8%, Eg ∼ 2.05 eV) achieves an efficiency of 7.9%, even in the absence of a window layer. This GaNP solar cell's efficiency is 3× higher than the most efficient GaP solar cell to date and higher than other solar cells with similar direct bandgap (InGaP, GaAsP). Through a systematic study of the structural, electrical, and optical properties of the device, efficient broadband optical absorption and enhanced solar cell performance are demonstrated.

Impact of concentrated solar radiation on a GaAs/AlGaAs Heterojunction Photo Converter with a limited absorption layer

The photoelectric and thermal properties of a GaAs/AlGaAs Heterojunction Photo Converter (HPC) with a GaP substrate within the range of the solar radiation concentrations Kc = 1–100 in a passive heat removal mode were studied. It was revealed that the limitation of the cumulative thickness of GaAs up to 5mkm in the heterojunction structure and wide zone GaP with comparatively high thermal conductivity between the p–n transition and heat removal contributes to the almost twice the reduction of the temperature growth of the p–n transition compared to a traditional GaAs/AlGaAs heterojunction photo converter.

Electrically tunable spectral responsivity in metal–semiconductor–metal photodetectors based on low-dimensional ZnCdS/ZnMgS/GaP, ZnCdS/ZnS/GaP heterostructures

We report on growth, fabrication and characterization of metal–semiconductor–metal (MSM) photodetectors based on periodic heterostructures with ZnCdS quantum wells separated by ZnMgS and ZnS barrier layers. Heterostructures were grown on semi-insulating GaP substrates by MOVPE. MSM-diodes with width of Ni–Au interdigitated Schottky barrier contacts and gap between them of 3μm and total detector area of 100×100μm2 have been fabricated. Detecting properties of MSM-heterophotodiodes have been investigated. We observe electrically tunable spectral response of these detectors. At low bias detectors provide narrowband response (FWHM=18nm at the wavelength 350nm) determined by a composition of ZnCdS quantum well. Increasing bias up to 70V shifts maximum detector sensitivity at the wavelength 450nm while narrowband response at 350nm remains. Thus, a two-color detection of light emission is provided.

Okazaki fragment maturation involves α-segment error editing by the mammalian FEN1/MutSα functional complex.

During nuclear DNA replication, proofreading-deficient DNA polymerase α (Pol α) initiates Okazaki fragment synthesis with lower fidelity than bulk replication by proofreading-proficient Pol δ or Pol ε. Here, we provide evidence that the exonuclease activity of mammalian flap endonuclease (FEN1) excises Pol α replication errors in a MutSα-dependent, MutLα-independent mismatch repair process we call Pol α-segment error editing (AEE). We show that MSH2 interacts with FEN1 and facilitates its nuclease activity to remove mismatches near the 5' ends of DNA substrates. Mouse cells and mice encoding FEN1 mutations display AEE deficiency, a strong mutator phenotype, enhanced cellular transformation, and increased cancer susceptibility. The results identify a novel role for FEN1 in a specialized mismatch repair pathway and a new cancer etiological mechanism.

Admittance spectroscopy of solar cells based on GaPNAs layers

Admittance spectroscopy is used to study defect levels in the layers of a GaPNAs quaternary solid solution. Centers with an activation energy of 0.22 eV and a capture cross section of ∼2.4 × 10−15 cm2 are found in doped n-GaPNAs layers grown on GaP substrates. These centers correspond to already known SiGa + VP defects in n-GaP; annealing decreases their concentration by several times. A level with an activation energy of 0.23–0.24 eV and capture cross section of ∼9.0 × 10−20 cm2 is found in undoped GaPNAs layers grown on Si and GaP substrates. The concentration of these centers substantially decreases upon annealing, and, at annealing temperatures exceeding 600°C, there is absolutely no response from these defects. For undoped GaPNAs layers grown on GaP substrates, a level with an activation energy of 0.18 eV and capture cross section of ∼1.1 × 10−16 cm2 is also found. The concentration of these centers remains unchanged upon annealing.

Photoluminescence of heterostructures with GaP1 − x N x and GaP1 − x − y N x As y layers grown on GaP and Si substrates by molecular-beam epitaxy

The structural and optical properties of heterostructures containing GaP1 − xNx ternary and GaP1 − x − yNxAsy quaternary alloy layers are discussed. The heterostructures are grown by molecular-beam epitaxy on GaP and Si substrates. The structures are studied by the high-resolution X-ray diffraction technique and photoluminescence measurements in a wide temperature range from 10 to 300 K. In the low-temperature photoluminescence spectra of the alloys with a low nitrogen fraction (x < 0.007), two clearly resolved narrow lines attributed to the localized states of nitrogen pairs and the phonon replicas of these lines are observed.

Structural and phase transformation of A III B V(100) semiconductor surface in interaction with selenium

Surfaces of GaAs(100), InAs(100), and GaP(100) substrates thermally treated in selenium vapor have been investigated by transmission electron microscopy and electron probe X-ray microanalysis. Some specific features and regularities of the formation of A3IIIB4VI (100)c(2 × 2) surface phases and thin layers of gallium or indium selenides A2IIIB3VI (100) on surfaces of different AIIIBV(100) semiconductors are discussed within the vacancy model of surface atomic structure.

GaP Homojunction LEDs Fabricated by Dressed-Photon-Phonon-Assisted Annealing

By using a homojunction-structured GaP single crystal, we generated a photon energy higher than the bandgap energy (2.26 eV). The device was fabricated by performing dressed-photon-phonon- (DPP-) assisted annealing, while applying a forward-bias current, on a p-n homojunction structure formed by implanting a dopant (Zn) into an n-type GaP substrate. The DPP-assisted annealing increased the light emission intensity in an energy band above 2.32 eV by at least 550% compared with that before annealing.

Effect of the nitrogen incorporation and fast carrier dynamics in (In,Ga)AsN/GaP self-assembled quantum dots

We report on the structural and optical properties of (In,Ga)AsN self-assembled quantum dots grown on GaP (001) substrate. A comparison with nitrogen free (In,Ga)As system is presented, showing a clear modification of growth mechanisms and a significant shift of the photoluminescence spectrum. Low temperature carrier recombination dynamics is studied by time-resolved photoluminescence, highlighting a drastic reduction of the characteristic decay-time when nitrogen is incorporated in the quantum dots. Room temperature photoluminescence is observed at 840 nm. These results reveal the potential of (In,Ga)AsN as an efficient active medium monolithically integrated on Si for laser applications.

Spatially resolved In and As distributions in InGaAs/GaP and InGaAs/GaAs quantum dot systems

InGaAs quantum dots (QDs) on GaP are promising for monolithic integration of optoelectronics with Si technology. To understand and improve the optical properties of InGaAs/GaP QD systems, detailed measurements of the QD atomic structure as well as the spatial distributions of each element at high resolution are crucial. This is because the QD band structure, band alignment, and optical properties are determined by the atomic structure and elemental composition. Here, we directly measure the inhomogeneous distributions of In and As in InGaAs QDs grown on GaAs and GaP substrates at the nanoscale using energy dispersive x-ray spectral mapping in a scanning transmission electron microscope. We find that the In distribution is broader on GaP than on GaAs, and as a result, the QDs appear to be In-poor using a GaP matrix. Our findings challenge some of the assumptions made for the concentrations and distributions of In within InGaAs/GaAs or InGaAs/GaP QD systems and provide detailed structural and elemental information to modify the current band structure understanding. In particular, the findings of In deficiency and inhomogeneous distribution in InGaAs/GaP QD systems help to explain photoluminescence spectral differences between InGaAs/GaAs and InGaAs/GaP QD systems.

Large interface diffusion in endotaxial growth of MnP films on GaP substrates

The metal organic vapor deposition of MnP films on GaP (100) substrates is shown to have a substantial endotaxial component. A study of the growth time evolution of the endotaxial depths of MnP grains reveals a diffusion-controlled growth with a relatively large diffusion coefficient of Mn in GaP. The value (2.2 ± 1.5) × 10−15 (cm2/s) obtained at 650 °C is at least two orders of magnitude larger than the reported Mn diffusion in bulk GaP. GaP surface mounds provide further indirect evidence that this large diffusion coefficient is concurrent with the out-diffusion of Ga atoms at the growing MnP/GaP interface. No trace of dislocations could be observed at or near this interface, which strongly suggests that Mn diffusion occurs through vacant sites generated by the difference between the crystallographic structures of MnP and GaP.

Design of Next Generation Full Spectrum Solar Cells Using Intermediate Band Semiconductors

The intermediate band solar cell (IBSC) is an attractive concept to achieve photovoltaic conversion efficiencies exceeding the Shockley-Quiessar efficiency limit for a single junction cell. In an IBSC, a partially occupied energy band located within the bandgap region of a semiconductor serves as a ‘stepping stone’ for the absorption of lower energy photons that are nominally not absorbed by the cell. In theory, the addition of this ‘intermediate band’ would provide a high photocurrent while maintaining a high output voltage.1 Recently, an IBSC device using the highly-mismatched semiconductor GaNAs alloy (HMA’s) has demonstrated optical activity from the three energy bands and is a proof of principle for the IBSC concept.[2] It has been proposed that the GaAsPN dilute nitride alloy system is another promising candidate material for IBSC’s.3 Calculations based on the band anticrossing model4 show that the intermediate band formed by the localized N level in GaNxAsyP1-x-y alloys with y<0.7 will be narrow and completely separated from the conduction band and hence more suitable as an intermediate band semiconductor for IBSC’s.3 The location of the IB (E-) and the conduction band (E+) of this material system can be tuned more effectively for optimal absorption of the solar spectrum by changing the As/P ratio (y).. Furthermore, GaAsyP1-y exhibits a direct-indirect gap crossover at approximately y=0.5, and for alloys with compositions y>0.5 the photon absorption occurs at the lower energy Γ band, yet electron transport may take place in the indirect X band. This could result in an IBSC absorber material with a high absorption coefficient that retains long carrier lifetimes.5 This work presents the design and characterization of a GaAsPN-based IBSC device. In order to fabricate a functioning IBSC device, first p-type, and n-type GaNAsP were grown and characterized in terms of their optical and electrical properties. We found that efficient p and n-type doping of GaNAsP can be achieved with Be and Si, respectively. Next, GaAsPN-based IBSC devices were grown by gas-source molecular beam epitaxy (MBE) on GaP substrate with a thick (~1.5µm) compositionally graded GaAsP buffer layers. Both a blocked intermediate band structure, where the intermediate band is electrically isolated from the valence and conduction bands, and an unblocked intermediate band structure (as a reference structure) were considered. The design of the structure was optimized to achieve efficient charge-carrier extraction, yet still demonstrate absorption from the three possible band-to-band transitions.The external quantum efficiency, both with and without a white-light bias, was used to evaluate the spectral response of the devices and the optical activity of the intermediate band. I-V measurements using both AM 1.5 and under 30x concentration were used to evaluate the PV device performance.[1] Luque, A., Marti, A. & Stanley, C. Understanding intermediate-band solar cells. Nature Photonics 6, 146–152 (2012).[2] López, N., Reichertz, L., Yu, K.M., Campman, K. & Walukiewicz, W. Engineering the Electronic Band Structure for Multiband Solar Cells. Phys. Rev. Lett. 106, 028701 (2011).[4] Shan, W. et al. Band anticrossing in GaInNAs alloys. Phys. Rev. Lett. 82, 1221–1224 (1999).[5] Yu, K. M. et al. Multiband GaNAsP quaternary alloys. Appl. Phys. Lett 88, 092110 (2006).[6] Y. J. Kuang, et al. GaNAsP: An intermediate band semiconductor grown by gas-source molecular beam epitaxy, Appl. Phys. Lett. 102, - (2013).

Analysis of the core–shell interface between zinc-blende GaP and wurtzite ZnO

Core–shell GaP/ZnO nanowires (NWs) were prepared in a two-step process: (1) GaP NWs were grown on GaP substrate by low-pressure metalorganic vapour phase epitaxy using 30nm Au seeds as nucleation centres, (2) the GaP NWs were covered in a thin nanocrystalline Ga-doped ZnO layer by sputtering in a Perkin Elmer planar RF diode system. Electrical contacts were processed to individual GaP/ZnO NWs using electron beam lithography, evaporation and lift-off of metallic layers: Au/Zn (GaP core) and Au/Al (ZnO shell). Electrical and photocurrent measurement of the NWs confirmed that a radial pn heterojunction was formed between the GaP core and ZnO shell.

Defect selective etching of GaAsyP1−y photovoltaic materials

Rapid and accurate threading dislocation density (TDD) characterization of direct-gap GaAsyP1−y photovoltaic materials using molten KOH defect selective etching (DSE) is demonstrated. TDDs measured using molten KOH DSE show close agreement with those from both electron beam-induced current mapping and planar view transmission electron microscopy, provided TDD<107cm−2. H3PO4 DSE is also demonstrated as an accurate method for characterizing TDD of GaP substrates. Taken together, the DSE methods described here enable TDD characterization over large areas (>105µm2) from substrate to GaAsyP1−y device layer.

A novel Hemispherical Dielectric Resonator Antenna on an Electromagnetic Band Gap substrate for broadband and high gain systems

In this paper we propose and investigate the application of Electromagnetic Band Gap (EBG) substrate for improving the performance of Hemispherical Dielectric Resonator Antenna (HDRA). Our designed EBG shows a band gap in the frequency range of 1.75–2.25GHz and the HDRA is resonant at 2GHz which falls within the bandgap of the EBG. When combined with the EBG substrate the −10dB bandwidth shows an improvement from 11.25% to 30%. On engineering the height of the HDRA on EBG substrate the gain is improved from 6.13dBi to 9dBi. To validate the results, simulations are carried out on CST Microwave Studio and HFSS.

Study of ZnO nanostructures grown by a hydrothermal process on GaP/ZnO nanowires

ZnO is a prominent material for creation of nanostructures as a multifunctional material for broad applications in blue and ultraviolet optoelectronics. A lot of efforts have been dedicated to understand the unique properties of nanostructured materials. The main purpose of this work is to verify (1) the technology of thin ZnO films deposition by RF magnetron sputtering to cover round GaP nanowires prepared by metalorganic vapor phase epitaxy, and (2) the hydrothermal growth of core/shell ZnO nanostructures on both GaP/ZnO and GaP/ZnO structures and nanowires deposited by RF magnetron sputtering. SEM, XRD, optical ellipsometry and micro-Raman measurements were employed to investigate the structural and optical properties of GaP/ZnO structures as well as core/shell nanostructures. The thickness, columnar structure and surface layer roughness of the deposited ZnO layers were estimated from cut-edge SEM images and verified by spectral ellipsometry. The measured XRD intensity patterns of (002) ZnO line of hydrothermally grown ZnO nanoclusters on nanowires show a narrow spectral width ∼0.17° which indicates a good crystalline structure in comparison with ZnO films prepared by magnetron sputtering on GaP substrate, even after their annealing. The PL spectra of the hydrothermally grown GaP/ZnO core/shell nanostructure show typical near band emission and very strong yellow broadband emission from Zn(OH)2 or hydroxyl groups for ZnO structures. For the first time we have demonstrated formation of GaP/ZnO core/shell nanostructured arrays on GaP nanowires grown by hydrothermal process.

Composition determination of quaternary GaAsPN layers from single X-ray diffraction measurement of quasi-forbidden (002) reflection

GaAsPN layers with a thickness of 30 nm were grown on GaP substrates with metalorganic vapor phase epitaxy to study the feasibility of a single X-ray diffraction (XRD) measurement for full composition determination of quaternary layer material. The method is based on the peak intensity of a quasi-forbidden (002) reflection, which is shown to vary with changing arsenic content for GaAsPN. The method works for thin films with a wide range of arsenic contents and shows a clear variation in the reflection intensity as a function of changing layer composition. The obtained thicknesses and compositions of the grown layers are compared with accurate reference values obtained by Rutherford backscattering spectroscopy combined with nuclear reaction analysis measurements. Based on the comparison, the error in the XRD defined material composition becomes larger with increasing nitrogen content and layer thickness. This suggests that the dominating error source is the deteriorated crystal quality due to the nonsubstitutional incorporation of nitrogen into the crystal lattice and strain relaxation. The results reveal that the method overestimates the arsenic and nitrogen content within error margins of about 0.12 and about 0.025, respectively.

A theoretical investigation of the band alignment of type-I direct band gap dilute nitride phosphide alloy of GaNxAsyP1–x–y/GaP quantum wells on GaP substrates

The GaP-based dilute nitride direct band gap material Ga(NAsP) is gaining importance due to the monolithic integration of laser diodes on Si microprocessors. The major advantage of this newly proposed laser material system is the small lattice mismatch between GaP and Si. However, the large threshold current density of these promising laser diodes on Si substrates shows that the carrier leakage plays an important role in Ga(NAsP)/GaP QW lasers. Therefore, it is necessary to investigate the band alignment in this laser material system. In this paper, we present a theoretical investigation to optimize the band alignment of type-I direct band gap GaNxAsyP1–x–y/GaP QWs on GaP substrates. We examine the effect of nitrogen (N) concentration on the band offset ratios and band offset energies. We also provide a comparison of the band alignment of type-I direct band gap GaNxAsyP1–x–y/GaP QWs with that of the GaNxAsyP1–x–y/AlzGa1–zP QWs on GaP substrates. Our theoretical calculations indicate that the incorporations of N into the well and Al into the barrier improve the band alignment compared to that of the GaAsP/GaP QW laser heterostructures.

Analysis of Annular Ring Microstrip Antenna with Air Gap and Uniaxial Substrate Superstrate Layers

Analysis of superstrate loaded, air gap tuned annular ring microstrip antenna is performed and effects of air gap tuning on the resonant frequency are investigated. Results obtained indicate that due to air gap tuning, resonant frequency can be incrementally or decrementally changed depending on the adjustment of anisotropy ratio of substrate and superstrate layers. Results can be used to obtain tunable, wideband antenna operation.