Band Gap Of InP Research Articles

Electrical activity of Yb in InP

We have performed EPR measurements in synthesised InP: Yb characterised by Hall effect, SSMS and SIMS analysis and by PL experiments. In our n-type samples we observed resonance due to the Yb3+ ground state; we deduce that the acceptor Yb2+ level is not in the InP bandgap.

Determination of the PIn antisite structure in InP by optically detected electron-nuclear double resonance.

Optically detected electron-nuclear double resonance (ODENDOR) is reported for the ${\mathrm{P}}_{\mathrm{In}}$ antisite in p-type InP. In both electron-irradiated and as-grown samples, ENDOR signals from the four nearest P neighbors and the next In shell were detected by monitoring radio-frequency-induced changes in magnetic circular dichroism associated with absorption near the band edge of InP while maintaining microwave resonance of the ${\mathrm{P}}_{\mathrm{In}}$ antisite. The electronic wave function of the ${\mathrm{P}}_{\mathrm{In}{}^{+}}$ state is highly localized, essentially all of it accounted for within these first two neighbor shells. The optical-absorption band associated with the antisite is centered above the InP band gap, and only its tail is observed.

Mechanism for annealing-induced changes in the electrical characteristics of Al/GaAs and Al/InP Schottky contacts

We report a systematic study of the electrical properties of Al diodes formed on GaAs (110) and InP (110) surfaces. Intimate Schottky barrier diodes were fabricated by in situ metal deposition in ultrahigh vacuum on atomically clean cleaved n-type and p-type surfaces. Current–voltage (I–V) measurements as a function of temperature were performed to determine the Schottky barrier heights using thermionic emission theory. For the unannealed Al diodes, our results indicate that the interface Fermi level of n-type and p-type samples pins at essentially the same position within the band gap of GaAs and InP. Annealing-induced changes in the electrical characteristics of the Al diodes can be completely accounted for by a shift in the Fermi level pinning position toward the valence band maximum of the GaAs and InP. We show that this is the only possible alternative because the annealing-induced increase in the barrier height of the diodes formed on n-type material is equal in magnitude to the decrease in the barrier height of the diodes formed on p-type material. Previous reports have attributed the increase in the apparent barrier height of n-type samples, which occurs upon annealing, to the formation of a larger band-gap semiconductor at the interface (i.e., AlxGa1−xAs and AlxIn1−xP) or to changes in the current transport process due to an increased rate of trapping carriers at deep levels near the interface. These mechanisms can be ruled out because they are inconsistent with the new data for diodes formed on p-type material. Because of the unique properties of Al and its interaction with the semiconductor substrate, we show that the results of this study provide a particularly critical test of different models of the Schottky barrier.

Transport properties and persistent photoconductivity in InP/In0.53Ga0.47As modulation-doped heterojunctions

This paper reports a study of the electrical properties of a systematic series of InP/In0.53Ga0.47As modulation-doped heterostructures grown by metalorganic chemical vapor deposition. Both Hall-effect and Shubnikov–de Haas measurements are used to obtain consistent values for carrier densities and mobilities. The heterostructures are shown to display a persistent photoconductive effect at low temperatures (<80 K) which results in changes in both the carrier density and the mobility. The variation of mobility with carrier density is analyzed to show that alloy disorder and background charged impurity scattering are the dominant scattering mechanisms. Excitation across the InP band gap is shown to be necessary for the persistent photoconductivity. We propose a mechanism for this effect in which electron hole pairs created by illumination are separated by electric fields built into the heterojunction with the holes subsequently being trapped in the InP substrate.

Doping superlattices in organometallic vapor phase epitaxial InP

Doping superlattices (nipi structures) have been grown in InP using organometallic vapor phase epitaxy in an atmospheric pressure reactor using trimethylindium and phosphine in a hydrogen ambient. The n-type and p-type dopants were diethyltellurium and dimethylzinc, respectively. The 4-K photoluminescence spectra at various excitation intensities are presented for a structure consisting of six 200-Å layers with doping levels of 1×1018 and 2×1018 cm−3 for the n and p layers. The luminescence peak is found to occur at energies considerably less than the band gap of InP and to move to higher energies with increased excitation intensity, as expected for doping superlattices where the band gap, which is indirect in real space, increases with increasing excited carrier concentration. The total photoluminescence signal decays in several steps, each exponential, with time constants ranging from 6×10−8 to 7×10−4 s at 4 K, typical of these spatially indirect band-gap materials.

Electrical properties of Al 2O 3 and AlP xO y dielectric layers on InP

Al 2O 3 and AlP x O y dielectric layers have been deposited on n-type InP substrates and the electrical properties of the interfaces have been evaluated by current-voltage and capacitance-voltage ( C-V) measurements on metal- insulator-semiconductor diodes. Layers were deposited by combining trimethyl- aluminum, oxygen and phosphine in a low pressure chemical vapor deposition reactor in which the oxygen was excited in an r.f. plasma prior to mixing with the reactive gases in the deposition zone. The Al 2O 3 layers were invariably too conductive for meaningful C-V measurements; however, the AlP x O y layers not only were of high resistivity (ϱ > 10 16 Ω cm) but also exhibited interfacial properties superior to those of SiO 2 layers on InP. The surface potential could be modulated over the full band gap of InP since the surface density was less than 10 11 cm -2 eV -1 over much of the band gap.

Hot carrier injection of photogenerated electrons at indium phosphide–electrolyte interfaces

Hot electron reduction of p-nitrobenzonitrile at (111) p-InP in acetonitrile electrolyte was observed as a supraband-edge redox reaction. The band-edge positions of the p-InP electrode were unequivocally established from Mott–Schottky data obtained as a function of light intensity and frequency. Special conditions of low light intensity and electrode potential were found wherein the semiconductor band edges were either fixed or had moved only very slightly with respect to redox potentials in the electrolyte, such that the respective supraband-edge redox reactions were definitely outside the band gap of InP.

Investigation of InP surface and metal interfaces by surface photovoltage and Auger electron spectroscopies

We have used surface photovoltage spectroscopy (SPS) and Auger electron spectroscopy (AES) to investigate the extrinsic surface states produced within the InP band gap by a variety of wet chemical treatments as well as by UHV metal chemisorption, oxidation, and Ar+ bombardment. UHV-cleaved surfaces display no intrinsic surface states, only extrinsic states associated with an excess of surface P. We have attempted to correlate the various SPS features with the chemical composition of these surfaces, particularly with KAg(CN)−2 -treated surfaces, for which the surface recombination velocity on p-InP is known to decrease significantly.

Correlation of Fermi-level energy and chemistry at InP(100) interfaces

X-ray photoemission spectroscopy data are used to correlate the interface Fermi-level pinning energy EiF and the corresponding interface chemistry for n-type and p-type InP (100) samples simultaneously subjected to a series of surface treatments. Interfaces of Schottky-barrier contacts formed during a sequence of Au and of Al depositions made both onto chemically etched and thermally cleaned InP surfaces were investigated. Changes in EiF of up to ∼0.6 eV in the upper half of the InP band gap occurred in response to changes in interface chemistry. The observed behavior of EiF is interpreted in terms of a single defect model with multiple charge states.

Effect of grain boundaries on the minority carrier diffusion length in InP solar cells

A minority carrier diffusion length inhomogeneity induced by grain boundaries on indium tin oxide/CdS/InP and indium tin oxide/InP polycrystalline solar cells has been investigated. The open-circuit voltage method has been employed and scanning surface photovoltage measurements have been carried out. By illuminating selected areas of the devices with a light of low intensity whose energy was varied in a narrow spectral range above the energy band gap of InP, a decrease in the diffusion length corresponding to the grain boundary position was detected. An explanation of the limited conversion efficiency achieved in these solar cells has been partially ascribed to the presence of a high grain boundary interface states density within high angle grain boundaries.

Fermi-level pinning and chemical structure of InP–metal interfaces

We have used soft x-ray photoemission spectroscopy (SXPS) to investigate the dependence of Fermi-level pinning on chemical structure at InP–metal interfaces. SXPS core level spectra of Al, Ti, Ni, Au, Pd, Ag, and Cu on UHV-cleaved InP(110) surfaces reveal evidence for semiconductor outdiffusion, metal indiffusion, metal-anion bonding and metal-cation alloying. Corresponding Fermi-level movements indicate a range of pinning positions at significantly different energies within the n-type InP band gap. These results demonstrate that the Schottky barrier heights depend sensitively on changes in interface chemical bonding and diffusion, which strongly affect the type of electrically active sites and interfacial layers formed.

The Al-(n-InP) Schottky barrier

Schottky barriers have been prepared by the evaporation of aluminium on to bulk-grown n-type InP slices. Reproducible devices were obtained providing sufficient care was taken over the preparation of the semiconductor surface. Current-voltage, capacitance-voltage and photocurrent measurements were made on the diodes. The current measurements showed the ideality factor n, to be close to unity at room temperature and above, indicating that the main mechanism of current flow was thermionic emission. Below room temperature, the ideality factor increased. The capacitance measurements indicated the presence of a deep donor about 1 eV below the conduction band edge. All three measurement techniques gave a calculated value of Schottky barrier height in the region of 0.5 eV. The variation of barrier height with temperature was found to be 4*10-4 eV K-1, which corresponds closely with the temperature variation of the band-gap of InP.

Optical and capacitance spectroscopy of InP:Fe

Photocapacitance, DLTS, optical absorption and photoluminescence data are presented for iron- and iron-germanium-doped Czochralski single-crystal InP. The results demonstrate that the Fe2+ to Fe+ transition is not present within the InP band gap. A feature observed in photocapacitance and optical DLTS is attributed to the presence of the Fe4+ charge state, and features associated with the well known Fe3+ and Fe2+ states also occur. Photoluminescence measurements show an iron-related band near 0.5 eV, not previously reported in the literature.

Electroluminescent p-InP/n-CdS heterodiodes

p-InP/n-CdS heterodiodes electroluminesce under forward bias. In diodes prepared by in vacuo growth of CdS layers on InP substrates, the spectrum is determined by recombination through deep interface states. Anneals at 500–600 °C shift the emission to energies close to the band gap of InP.

PHOTOEMISSION FROM InP-Cs-O

Photoelectric measurements on cleaved p+ InP show that a process of cesiation and oxidation can produce a work function lower than the InP bandgap. Efficient photoemission results, with luminous efficiencies of 450 μA/lumen or better, and a threshold at 1.24 eV (1 μ).