Semi-insulating GaP Research Articles

The Features of GaAs and GaP Semiconductor Cathodes in an Infrared Converter System

The aim of this study is to examine the electrical and optical comparative analysis of semi-insulating GaAs and GaP photoconductive electrodes in an infrared converter system with a resistivity of >107 Ω cm for the same interelectrode distance d and gas pressure p experimentally and theoretically, when the discharge cell has been filled by argon. To provide the stability of the semiconductor electrode in Ar media, the experiments were carried out in Townsend and glow discharge regimes for various parameter sets of pressure, interelectrode gap and discharge voltage. When the discharge exceeds a critical voltage value, some N-shape CVCs, which stem from both semiconductors and Ar gas, have been observed. To compare the features of the GaAs and GaP cathodes, the COMSOL multiphysics programme is used under the Ar media. The mean electron energy, thermal velocity, surface charge density, space charge and initial electron densities, and electron mobilities have been calculated for both semiconductor materials. It has been found that the electron mobility μe, electron thermal velocity, surface charge density σ and mean electron energy of GaAs is higher than those of GaP; hence, GaAs has better opto-electronic features compared to GaP. In addition, the experiments on the optical explorations prove that GaAs exhibit better optical response in the infrared region. The explored transport characteristics of the semiconductor electrodes are of importance, and they have to be taken into account when studying plasma cells.

Wavelength selective UV/visible metal-semiconductor-metal photodetectors

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. Detecting properties of the MSM-heterophotodiodes have been investigated. We observe electrically tunable spectral response of these detectors. At low bias detectors provide narrowband response at the wavelength 350 nm with FWHM = 18 nm. Increasing bias shifts maximum detector sensitivity at the wavelength 450 nm while narrowband response at 350 nm remains. Thus, a two-color detection of light emission is provided.

Selective UV radiation detection on the basis of low-dimensional ZnCdS/ZnMgS/GaP and ZnCdS/ZnS/GaP heterostructures

The detecting properties of periodic heterostructures with ZnCdS quantum wells separated by ZnMgS or ZnS barrier layers are studied. Heterostructures are grown on semi-insulating GaP substrates by metal organic vapor-phase epitaxy (MOVPE). On their basis, metal–semiconductor–metal (MSM) diodes with interdigital Schottky contacts 3 μm, distances between them of 3 μm, and a total detector area of 100 × 100 μm are fabricated. The detectors have low dark currents (10–12 A); at low bias voltages, they provide a narrow- band response (full-width at half-maximum of FWHM = 18 nm at a wavelength of 350 nm) which is controlled by the ZnCdS quantum-well composition. As bias is increased to 70 V, the maximum detector sensitivity shifts by a wavelength of 450 nm, which is caused by penetration of the external-bias electric field into the semi-insulating GaP substrate. In this case, the narrow-band response of the detector at a wavelength of 350 nm is retained, i.e., the two-color detection of light is provided.

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.

Strain relief and growth optimization of GaSb on GaP by molecular beam epitaxy

In this paper, the impact of growth parameters on the strain relaxation of highly lattice mismatched (11.8%) GaSb grown on GaP substrate by molecular beam epitaxy has been investigated. The surface morphology, misfit dislocation and strain relaxation of the GaSb islands are shown to be highly related to the initial surface treatment, growth rate and temperature. More specifically, Sb-rich surface treatment is shown to promote the formation of Lomer misfit dislocations. Analysis of the misfit dislocation and strain relaxation as functions of the growth temperature and rate led to an optimal growth window for a high quality GaSb epitaxial layer on (001) GaP. With this demonstrated optimized growth, a high mobility (25 500 cm2 V −1 s−1 at room temperature) AlSb/InAs heterostructure on a semi-insulating (001) GaP substrate has been achieved.

RF- in electric fields studies of GaP

Abstract We report on combined RF- μ SR and electric fields (EF) μ SR measurements in semi-insulating GaP. At low temperature the capture of excess carriers by a neutral muonium ( Mu = μ + + e - ) center is suggested to be a dominant process in muonium charge dynamics. The charged muonium fraction ( Mu - or Mu + ) formed on the microsecond time-scale is increased with lowering the temperature. Contrary to the usually observed scenario, at T 40 K an EF prevents formation of the final charged state.

Dynamics of T-site muonium states in gallium phosphide

Abstract We report on the motional dynamics of Mu - and the ionization processes related to the Mu T acceptor state in n-type gallium phosphide. Muon spin resonance results on semi-insulating GaP suggest the presence of both Mu + and Mu - diamagnetic states above ∼ 400 K . From the growth step in the RF amplitudes, we obtain an energy of ∼ 0.82 eV for the Mu T acceptor-related hole ionization. The loss of the Mu - RF-component above 600 K yields an energy of ∼ 1.7 eV , which is assigned to thermal promotion of an electron from Mu - to the conduction band. These two results locate the Mu T acceptor level with respect to the valence and conduction band edges, respectively. Low-field spin precession and zero-field depolarization data on n-type GaP show a peak in diamagnetic fraction below 300 K, and a roughly linear increase in amplitude at higher temperatures.

Weakly bound muonium state in GaP

Muonium formation via electron transport to a positive muon implanted into semi-insulating GaP has been studied using muon spin rotation/relaxation with alternating electric fields up to 160 kV/cm. Formation of the muonium ground state is prohibited by a characteristic electric field of about 50 kV/cm in GaP compared to 5 kV/cm in GaAs, implying that formation of the Mu ground state may proceed through a weakly bound intermediate state with a binding energy of about 23 meV in GaP or 7 meV in GaAs. These results are discussed and justified within the effective mass model.

Weakly bound muonium state in a semiconductor

Delayed muonium formation via electron transport to the positive muon in semi-insulating GaP has been studied using a muon spin rotation technique with alternating electric fields. The characteristic electric field of about 50 kV/ cm suggests that formation of a ground state muonium atom proceeds through an intermediate weakly bound hydrogen-like state. Results are justified within the framework of the effective mass approximation.

Research of spatial resolution in external electro-optic probing

A new method, based on zero point of longitudinal electric field, was used to determine the spatial resolution of external electro-optic (EO) probing equipment. Considering the diffraction of Gauss beam, the result of external EO probing was simulated which was in accordance with the experiment. A spatial resolution <1 μm was demonstrated initially in our equipment using 650 nm laser diode as probe beam and semi-insulating GaP as probe tip.

Raman spectroscopy of porous and bulk GaP subjected to MeV-ion implantation and annealing

Porous layers on (100)-oriented n-type liquid encapsulated Czochralski grown GaP crystals were fabricated by electrochemical etching in a H2SO4 aqueous solution and analyzed by scanning electron microscopy. C+12 ions were introduced at room temperature by 3 MeV energy implantation into porous and bulk samples at two ion doses of 1014 and 1015 cm−2. The prepared samples were annealed in the temperature range between 200 and 600 °C applying rapid thermal annealing (RTA) technique. A comparative micro-Raman study was carried out on the porous and bulk substances. Porosity was found to lead to the violation of the selection rules and to remarkable changes in the optical properties. Additionally, Fröhlich-type modes were observed in the Raman spectra of the porous layers. High energy implantation produces a thin high damaged layer, buried at the depth of the mean projected range. Implantation does not result in a drastic damage of the samples and they undergo a fast recovery after RTA. After this treatment a semi-insulating GaP layer is created, which is thermally stable up to 600 °C.

Photoluminescence from transmuted impurities in neutron-transmutation-doped semi-insulating GaP

The transmuted impurities Ge and S in neutron-transmutation-doped (NTD) semi-insulating GaP were studied by a photoluminescence method. A broad emission was observed at 1.65 eV accompanied by a hump at ∼1.87 eV in samples annealed above 640°C. These emissions are attributed to Ge Ga–Ge P complex and S donor–Ge acceptor pair recombination, respectively, indicating the presence of the transmuted impurities. The formation of the complex defect was examined using a configuration coordinate model. The presence of the complex defects restricted the electrical activation of the transmuted impurities in NTD-GaP, forming a localized state.

Resonant Mandelstam-Brillouin light scattering and Raman scattering in semiconductors with intermediate exciton states belonging to discrete exciton bands and the continuous spectrum

The results of a theoretical and experimental investigation of resonant Mandelstam-Brillouin light scattering by thermal acoustic phonons with k=0 near the direct absorption edge (in the case of ZnSe crystals) are analyzed. The appearance of a new type of resonant increase in the intensity of Raman scattering by optical phonons with k≠0, which corresponds to resonance with the scattered light in the output channel, near the indirect absorption edge (in the case of semi-insulating GaP:N crystals) is also reported. The resonant gain reaches ∼4×103 at frequencies corresponding to overtone scattering assisted by LO(X) and LO(L) phonons. Exciton states belonging to both discrete exciton bands and to the continuous spectrum are considered as the intermediate states involved in the scattering processes in calculations of the resonant scattering tensors. In addition, all the intraband transitions, as well as the interband transitions between the conduction band, the valence bands, and the spin-orbit split-off band are taken into account, and good agreement with the experimental results is obtained.

Poole–Frenkel effect assisted emission from deep donor level in chromium doped GaP

The electrical properties of chromium-related defects in GaP are investigated. Using deep-level transient spectroscopy, a related deep level is observed in p-type GaP exhibiting an activation energy, associated with hole emission, of 0.5 eV. Detailed capacitance transient investigations were undertaken to study the electric field dependence. This emission rate which is found to have a field dependence can be fitted by a Poole–Frenkel model. Evidence is given that the trap is the Cr4+/3+ deep donor level in GaP caused by substitutional Cr on Ga sites. This trap seems to be well adapted to compensate donors for the growth of the semi-insulating GaP.

Neutral manganese acceptor in GaP: An electron-paramagnetic-resonance study.

In order to clarify the nature of the neutral Mn acceptor in GaP, we have carried out optical-absorption and electron-paramagnetic-resonance (EPR) experiments using both conventional and thermally detected EPR on semi-insulating GaP:Mn. In thermal equilibrium at low temperatures, all the manganese occurs in the charged acceptor state ${\mathrm{Mn}}_{\mathrm{Ga}}^{2+}$(${\mathit{A}}^{\mathrm{\ensuremath{-}}}$). By illumination with photon energies greater than 1.2 eV, it can be partially converted into the neutral charge state. The arising photostimulated EPR spectrum shows the characteristic of a tetragonally distorted center with an integer spin. The resonance lines are detectable only at temperatures below 7 K, and their linewidth of about 50 mT is due to the unresolved Mn-hyperfine splitting. We interpret the experimental data in terms of ${\mathrm{Mn}}_{\mathrm{Ga}}^{3+}$ ions on strain-stabilized sites of tetragonal symmetry due to a strong T\ensuremath{\bigotimes}\ensuremath{\epsilon} Jahn-Teller coupling within the $^{5}$${\mathit{T}}_{2}$ ground state. Such a behavior is expected for a 3${\mathit{d}}^{4}$ defect, as observed for the isoelectronic impurity ${\mathrm{Cr}}^{2+}$ in GaAs, and other tetrahedrally coordinated semiconductors. The analysis of the EPR spectra thus verifies that, in GaP, the neutral charge state of the Mn acceptor is ${\mathrm{Mn}}_{\mathrm{Ga}}^{3+}$(${\mathit{A}}^{0}$) in contrast to its behavior in GaAs and InP. \textcopyright{} 1996 The American Physical Society.

Cadmium-hydrogen shallow acceptor complexes in germanium

The transmuted impurities Ge and S in neutron-transmutation-doped (NTD) semi-insulating GaP were studied by a photoluminescence method. A broad emission was observed at 1.65 eV accompanied by a hump at ∼1.87 eV in samples annealed above 640°C. These emissions are attributed to GeGa–GeP complex and S donor–Ge acceptor pair recombination, respectively, indicating the presence of the transmuted impurities. The formation of the complex defect was examined using a configuration coordinate model. The presence of the complex defects restricted the electrical activation of the transmuted impurities in NTD-GaP, forming a localized state.

Photorefractive and photochromic effects in undoped GaP at high temperature

Photorefractive and photochromic effects are investigated in undoped semi-insulating GaP at high temperature. The photochromic effect takes place at the temperature above 340 K and the depreciation of the photorefractive coupling coefficient is observed above 385 K. These results suggest the existence of additional donor and acceptor levels. The binding energy of the donor level is estimated to be 420 meV.

Temperature dependence of the photorefractive effect in GaP

The temperature dependence of the photorefractive two-beam coupling gain coefficient, its time constant, and the optical absorption in semi-insulating undoped GaP were measured. It was observed that at low temperature the two-beam coupling gain coefficient was quenched and the optical absorption exhibited a dependence on intensity. A multiple defect model for GaP which has a shallow donor level and a shallow acceptor level in addition to the photorefractive deep donor was presented. These secondary traps contribute significantly to the photorefractive effect and the absorption at low temperature. The binding energies of the shallow donor and the shallow acceptor were estimated from the experiments to be 150 meV and 120 meV, respectively.

New Aspects of (Semi-Insulating) GaP:Cu

buried Schottky contact model for the complex behavior of Cu in GaP. PIXE studies show that Cu can reach very high concentrations in that material. Channeling indicates that a part of the Cu forms precipitates. Hall measurements on sets of samples were made to examine the electrical trans port coefficients. The mobilities of the samples with the most abundant concentration of Cu were found to be dominated by a term ocT0·5 which was identified as a component induced by metallic spikes with non-overlapping depl etion zones. We come to the conclusion that Cu introduces an acceptor like defect as well as precipitates. For high initial carrier concentrations,

Electron spin resonance of antisite defects in as-grown and plastically deformed GaP

In as-grown GaP we investigated two phosphorous antisite related electron spin resonance spectra with respect to ligand hyperfine (lhf) interactions: basing upon a linewidth analysis, we attribute a hyperfine doublet with unresolved lhf structure (PA3) in n-GaP:S to a P-antisite defect with cubic symmetry. The lhf interaction of the well known lhf resolved PP4 doublet (PA1) in semi-insulating GaP:Cr was found to be temperature dependent. In plastically deformed GaP the two spectra showed contrary linewidth changes. In highly deformed n-GaP:S both signals were detectable. A new spectrum of low symmetry (GA1) was observed which we attribute to a gallium antisite related defect.