N-type GaP Research Articles

Carrier concentration profiles across GaP grain boundaries observed by raman measurements

Raman measurements are performed on grain boundaries in n-type and p-type GaP grown by the SSD method. The high-angle grain boundaries investigated show all a central region of carrier depletion (width about 20 μm) which is attributed to dopant depletion. Beside it exist broad ranges of carrier accumulation not always clearly pronounced. Possible reasons of the formation of these profiles are discussed.

Study of deep level centers at excited states in GaP by means of transient optical absorption spectroscopy

Transient optical absorption and luminescence induced by an electron pulse in n-type GaP and their changes induced by a subsequent laser pulse have been measured. It is shown that the decays of the optical absorption and of the luminescence induced by an electron pulse consist of a fast (F) component that decays within 1 ms and slow (S) components having a lifetime of about 10 ms. It is shown also that a laser pulse incident on the specimen after the F component is eliminated reduces the S component and produces the F component. The F component is ascribed to donor-acceptor recombination and the S component to annihilation of metastable centers.

Vacancy defects in as-grown and neutron irradiated GaP studied by positrons

Positron lifetime and Doppler-broadening measurements have been used to study vacancy defects in n-type GaP. Vacancies in the P sublattice with a concentration of some 1017 cm−3 were observed in as-grwon GaP. The vacancies disappear during annealing at 500–800 °C. In neutron-irradiated GaP positrons are trapped by Ga vacancies which anneal out in two stages situated at 300–550 °C and 550–700 °C.

Positron annihilation studies in alpha-irradiated n-type GaP

The positron annihilation technique has been used to study the defect recovery in 22.0 MeV alpha-irradiated n-type GaP. The increase in the lineshape parameter S along with defect specific parameter R between 200 and 350°C indicates the migration of vacancies and the formation of vacancy clusters. The defects start disappearing between 350 and 600°C.

Pressure dependence of shallow bound states in gallium arsenide

Photoluminescence and PL-excitation of high-purity n-type GaAs is reported at He temperatures and hydrostatic pressures of up to 80 kbar in diamond anvil cells. At low pressures intense PL aises from direct-gap free and bound excitons and band-to-acceptor transitions. Band structure becomes indirect at 41.3 kbar and spectra resemble n-type GaP. Weak indirect (X 1c)-gap recombination attributable to donor-bound-excitons and free excitons is identified. All bound states remain shallow and follow their band edges, thus giving the most precise Γ 1c-Γ 15v and X 1c-Γ 15v gap dependences on pressure (10.73 and -1.34 meV/kbar, respectively) yet reported. New indirect band gaps are derived for GaAs at atmospheric pressure.

High-temperature electron mobilities in LPE-Grown GaP

We report measurements to 500°C of resistivity and Hall mobility in Sn-doped, n-type GaP grown by liquid phase epitaxy. Samples with room-temperature carrier densities between 1 × 1016 and 1 × 1018cm−3 were studied. Mobilities were in the range 100–180 cm2/V-sec at room temperature and in the range 27–35 cm2/V-sec at 400°C. Carrier densities increased by only about a factor of two with increasing temperature. Theoretical fits to the mobility data were made by considering contributions from intervalley, polar-optic, acoustic-deformation-potential, and ionlzed-impurity scattering mechanisms. Our results confirm the utility of GaP for high-temperature device applications and provide important information on electrical parameters needed for device modeling and design.

The production and structure of the P-P3anti-site defect in electron-irradiated n-type GaP

Samples of n-type GaP doped with either (a) sulphur or (b) silicon to concentrations of about 1018 atoms/cm3 have been compared using EPR and IR measurements following a series of small doses of 2 MeV electron irradiation at room temperature. The EPR spectrum due to the (P-P3) antisite defect is produced up to a similar strength in both materials. The measurements suggest that it is unlikely that the defect involves an impurity. The authors speculate that the (P-P3) centre may be a gallium vacancy distorted to give (Vp-PGa) or a trigonal (VP-PGa-Gai) complex produced by a knock-on process.

A deep centre with excited states in MOVPE GaP grown under high phosphorus pressure

Using junction-space-charge techniques, a deep centre with excited states has been studied in undoped MOVPE n-type GaP grown under high phosphorus pressure. The ground-state and excited-state energy positions have been determined to be 0.82 and 0.16 eV below the conduction-band edge respectively. The photoionisation cross section for electrons shows a pronounced photo-thermal excitation behaviour. The kinetic properties of electron excitation and recombination are analysed using a model for two-step excitation. A method for determining the thermal activation energy of the dominant excited state is described. Comparing the results with those published previously, a possible relation of the centre to Ni(d9) is discussed.

Fabrication and characteristics of GaP photovoltaic cells

The GaP photovoltaic cells were fabricated as candidates for higher bandgap (2.26 eV) subcells of a high efficiency photovoltaic multi-cell system. The cell characteristics are investigated. Cells were fabricated by diffusing Zn as a p-type dopant into n-type GaP wafers. The best cell with silicon nitride AR coating exhibited the conversion efficiency ν of 7.6% with respect to the energy in a bandwidth of 0.35 μm ⪅ λ ⪅ 0.50 μ of the AM1 spectrum.

Temperature dependence of the hole lifetime in n-type GaP

The minority carrier lifetime has been measured at single dislocations in n-type GaP. From the temperature dependence of the dislocation lifetime we found a dominant recombination centre at a level 0.15eV which is, probably, associated with S-donor/Cu complexes.

Electroluminescence from LiInSe2-GaP heterodiodes

Heterodiodes have been prepared by evaporation of p-type LiInSe2 on n-type GaP. Typical diodes emit orange light (610 nm) under forward bias with external quantum efficiency of 10−4% at 77 K. Electroluminescence spectrum is coincident to the photoluminescence in LiInSe2 crystals.

Photothermal capacitance measurements on GaP:Ni

The photocapacitance spectrum of n-type GaP:Ni shows a peak near 0.74 eV and a rising edge at higher energies. The properties are consistent with the peak being due to photothermal ionisation to the conduction band via the excited state of the d9 configuration, while the rising edge is due to photoionisation directly from the d9 ground state to the conduction band. Experiment and theory agree that the effective capture rate of electrons is the same whether excitation is via the excited state or direct to the conduction band. A previously reported absorption process with threshold energy 0.78 eV is shown to be different from that giving the photocapacitance spectrum, and it is explained how one centre may dominate the absorption spectrum and a different one dominate the photocapacitance spectrum.

High brightness GaP green LED's

High brightness GaP green LED's have been developed by optimizing growth conditions to obtain a high quality p-n junction. In particular, the n-type GaP layer near the junction is greatly lowered in carrier concentration in order to decrease the nonradiative recombination center. The carrier concentration in the n-type GaP layer is decreased to 5-6 × 1015/cm3near the p-n junction and a minority-carrier lifetime of 800 ns (measured through the EL decay time) is obtained. The best device has a quantum efficiency of 0.45 percent at 12.5 A/cm^{2} with encapsulation. Excellent high-brightness LED lamps of 400 m Cd at a driving current of 20 mA can be obtained by using the high efficiency GaP green LED's.

Cyclotron resonance study of the conduction band in GaP

Far-infrared cyclotron resonance was observed in n-type GaP at high magnetic fields in the megagauss range. For magnetic fields parallel to the <100> axis, the second absorption peak was observed at 100 T in addition to the first peak at 23 T for a wavelength of 119 μm. The apparent cyclotron masses of electrons were thus determined to be m∗rmt = 0.254 ± 0.004 mo and m∗ℓ = 4.8 ± 0.5 mo at 119 μm. At 337 μm, on the other band, a broad absorption band was observed around 42 T besides the first peak at 8.0 T.

Compensation mechanism in Ni-diffused n-type GaP

Optical investigation of the diffusion profile of Ni acceptor in n-type Gap is presented. It is found that a single Ni impurity atom is responsible for compensation of 4 to 5 electrons from shallow donors. Generation of point defects, such as vacancies, by a dislocation climb mechanism is responsible for this large compensation.

Surface potential studies on Langmuir-Blodgett multilayers and adsorbed monolayers

The surface potential of multilayers of stearic acid, chlorophyll-a, cobalt-substituted chlorophyll and monolayers of a perfluorinated carboxylic acid deposited onto n-type GaP was measured by the Kelvin technique. A comparison is made between the surface potential of clean GaP and the surface potential of GaP onto which various numbers of layers of amphiphilic material have been deposited. The results can be interpreted in terms of a model in which all three materials deposited as multilayers contain p-type defects and a Schottky region thus exists both in the n-type GaP and also in the p-type multilayer.

Langmuir-Blodgett monolayers of preformed polymers on n-type GaP

We have shown that it is possible to vary the Schottky barrier height of GaP by varying the anhydride content of an insulating monolayer of poly(octadecene-1-maleic anhydride) deposited onto the semiconductor. This is attributed to negative charges on the anhydride groups, the surface state density being unchanged by the presence of a polymer monolayer.

Some electrical and photoelectric properties ofp-nstructures based on InP, AlSb, and GaP

An investigation was made of metal–oxide–semiconductor structures based on n- and p-type InP and of metal–insulator–semiconductor structures based on n-type InP and n-type GaP. Some of their parameters were estimated, including the nonlinear coefficient, barrier height, charge density, oxide thickness, electric field intensity, etc. It was found that in Au–n–InP structures the efficiency of conversion of incident light increased by 5–6%, compared with the usual InP structures, when the oxide layer thickness had the optimal value of ∼2.2–2.3 nm. The conversion efficiency obtained for the structures containing p-type InP and n-type AlSb was ∼10–14%.

Structural model of III–V compound semiconductor Schottky barriers

Schottky barriers have been fabricated on n-type GaP(111) crystals to study the structural characteristics of the diodes. The formation of Schottky barriers by evaporating a metal layer onto the III–V compound semiconductor surface generally created an amorphous film interlayer between the metal and the semiconductor. Current–voltage (I–V), capacitance–voltage (C–V) and Auger electron spectroscopy (AES) data were used to characterize the interface amorphous film. A model of a resistor in parallel with a capacitor and then in series with the metal and the semiconductor layers is used to describe the properties of a real Schottky barrier. The thickness of the amorphous film is in the range 50–500 Å, dependent on evaporation details. The dielectric constant and the resistivity of the amorphous film are experimentally estimated, and are found to be frequency dependent. A metal-amorphous film–semiconductor (MAS) configuration is proposed to be the structural model for a real Schottky barrier. The structural model is combined with the defect model to explain the fundamental transition in interface electronic nature between covalent and ionic semiconductors as well as other properties of a real Schottky barrier.

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.