InP Structures Research Articles

Structure of Sulphur-Passivated InP(100)-(1×1) Surface

ABSTRACTX-ray photoelectron spectroscopy, X-ray photoelectron diffraction, and S K edge X-ray absorption near-edge structure were used to characterize the air-stable S-passivated InP(100)-(lxl) surface prepared in (NH4)2S solution. The results show that one monolayer of sulphur which is bonded only to In is adsorbed on the surface. The S is found to occupy bridge-bonded sites, and the orientation of the In-S bond is determined to be in the [011] azimuth, with an In-S-In bridge-bond angle of about 100°.

Surface electron structure of InP(110) studied with angle-resolved photoelectron spectroscopy

The surface electron structure of InP(110) has been studied by means of synchrotron radiation excited angle-resolved photoelectron spectroscopy. After identifying the bulk-related spectral structures, the surface-induced energy bands have been mapped along symmetry directions. The polarization dependence of the surface-related structures is discussed.

Surface electron structure of InP(110) studied with angle-resolved photoelectron spectroscopy

Surface electron structure of InP(110) studied with angle-resolved photoelectron spectroscopy

Semi-insulating layers in InP obtained by Co or Fe ion implantation

Ion implanted Co or Fe into n-type InP produced semi-insulating (SI) layers over a wide range of ion doses. The I/V characteristics of vertical metal—SI InP—n-type InP structures demonstrated resistivities up to 6 × 102 Ω cm at low bias levels and current densities as low as 12 mA/cm2 at 2.5 V for 400keV ion energy implanted layers.

Characterization of interface states at III-V compound semiconductor-metal interfaces

Surface photovoltage spectroscopy (SPS) has been used for direct measurements of the extrinsic surface states within the band gaps of p-InP (110) and (100) and n-GaAs(110) before and after Al and Au deposition. The observed metal-induced surface states are found to pin the Fermi level at monolayer coverages at Ev+0.83 eV for Au/p-InP(110), Ev+1.10 eV for Al/p-InP(110), Ec−0.94 eV for Au/n-GaAs(110), and Ec−0.80 eV for Al/n-GaAs(110). The Au/Al/p-InP(110) structure, studied for the first time using SPS provides evidence of strong Al clustering upon the InP surface. Chemically etched and UHV-cleaved p-InP surfaces and Au interfaces are also compared. The correlation between the observed energy state positions and electrically measured Schottky barrier heights is discussed.

Fluorine-gas treatment of InP(100): physico-chemical characterization of the obtained components

Fluoride thin film InP (100) structures have been prepared by oxidization under fluorine gas for different temperatures and times. The composition of the obtained layers has been studied using various analytical techniques (Rutherford backscattering, infrared absorption and XPS). The bulk composition of the obtained layers is InF 3. Whatever the fluorination temperature ( T F) the formed phosphorus fluoride is eliminated during the reaction. An XPS study has shown that at the fluoride-InP interface, phosphorus, like indium, is chemically bound to fluorine. However it is demonstrated that for T F ⩽ 200 °C an important oxygen content, corresponding to absorbed water, is observed in the bulk of the fluoride thin films; on the contrary, for T F = 300 ° C, the grown InF 3 layers are insensitive to an ageing in moist air.

Conduction-band minima of InP: Ordering and absolute energies

Since the conduction-band structure of InP is still controversial, we perform an ab initio linear muffin tin orbital (LMTO) band structure calculation to obtain the valence bands with high accuracy. The LMTO is based on the local density approximation (LDA) which suffers from the well known ‘‘band-gap problem.’’ We therefore combine our calculated valence-band energies with carefully evaluated optical data from the literature and confirm the interconduction-band separation energies ΔEΓL=0.86±0.02 eV and ΔEΓX=0.96±0.02 eV. We also give new empirical local pseudopotential form factors adjusted to reproduce these experimental values.

Electronic and geometric structure of clean InP(001) and of the CaF2/InP(001) interface

In low-energy electron diffraction (LEED), we find two different reconstructions of the technologically important InP(001) surface, the well known (4×2) structure and a high temperature (4×2) structure with streaks at the half order spot positions which is interpreted as a disordered c(8×2) structure. The corresponding electronic structures were investigated by ultraviolet photoelectron spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS). For both types of reconstructions, we observe a surface state emission at the valence-band maximum and a strong fermi-level pinning. CaF2 was deposited onto these surfaces, and the interface formation was studied by LEED, UPS, and XPS. The overlayer grows epitaxially with (001) orientation of its bulk fluorite structure inspite of the large lattice mismatch of 7.5%. The electronic interface scheme with its valence-band discontinuity was deduced from photoemission measurements as a function of overlayer coverage. Band bending at the interface results from p-type defects.

OMVPE buried ultrafine periodic structures in GaInAs and InP

This paper describes fabrication methods for nanometer-pitch grating buried in the semiconductor for the future electron wave devices. Both wet chemical etching and selective growth are promising methods of grating formation on the surface of the semiconductor and also are damage-free processes. In the regrowth process to embed the grating, it is important to suppress the thermal deformation. Experimentally, InP corrugations 70nm-pitch grating were formed on InP surface in two ways — wet chemical etching and selective growth by OMVPE. InP gratings of 70nm pitch and 100nm depth were buried by OMVPE in GaInAs.

Surface-energy-induced mass-transport phenomenon in annealing of etched compound semiconductor structures: Theoretical modeling and experimental confirmation

A comprehensive model of the mass-transport phenomenon at the surface of compound semiconductors has been developed and experimentally confirmed. In the model, the effect of surface curvature on thermal decomposition and the resulting diffusion and regrowth has been formulated, and a differential equation has been derived that describes the temporal evolution of any (spatially) slowly varying surface profile during mass transport. The model predicts an exponential decay of sinusoidal profiles with a fourth power of spatial wavelength dependence, and a grading of single mesa steps with a fourth root of time dependence. Good agreement with the model has been obtained in a systematic experimental study employing etched structures in InP. This study yields the low value of 1.5 eV for the activation energy of the mass-transport process in InP.

Pressure-induced changes in the crystal structure and electrical properties of bulk InP

X-ray diffraction spectra and the electrical properties of bulk InP and InGaAs have been obtained in quenched samples after compressing them into metallic phases above 14 GPa. The x-ray diffraction spectrum of InP was similar to that of the zinc-blende phase, although the [200] reflection was missing and an extra line was observed near the [220] reflection. Transport measurements showed about three orders of magnitude decrease in carrier concentration from 1016 cm−3 before pressurization to 1013 cm−3 after pressurization. The electron mobility was similar to that found for X-conduction-band minima, and the resistivity was increased by about four orders of magnitude. The photoconductivity edge of the band-to-band absorption was quenched.

Lattice-mismatch-generated dislocation structures and their confinement using superlattices in heteroepitaxial GaAs/InP and InP/GaAs grown by chemical beam epitaxy

We report a detailed transmission electron microscopy and x-ray double-crystal diffractometry study of the lattice-mismatch-induced defect structures in InP grown on (100) GaAs substrate and vice versa by chemical beam epitaxy. A rough estimate of the dislocation densities in GaAs on InP is 2×1010 cm−2 at the interface and 5×107 cm−2 at the surface of the epilayer. The corresponding values in InP on GaAs are slightly lower as expected for the compressive stress state for InP. The majority of the dislocations lie on the {111} slip planes with 1/2 [110]- and 1/2 [101]-type Burgers vectors. A cross-grid-type interfacial misfit dislocation array is not observed. Instead, a complicated dislocation structure near the interface, consisting of overlapping pyramidal dislocation tangles (PDT) similar to those observed previously in InGaAs on InP caused by interfacial misfit particles, is presented. The interfacial dislocations form a cellular structure in GaAs on InP and a random structure in InP on GaAs. A Moiré fringe spacing study of InP on GaAs indicates a localized change in composition at the interface, possibly due to As incorporation or GaAs/InP intermixing. The formation of PDT defects and the variation in composition at the interface suggest a breakdown of layer-by-layer growth in the initial stage of growth which results in island nucleation. A dislocation mechanism for the PDT formation is also proposed. All epilayers prepared by chemical beam epitaxy (CBE) without two-stage growth are specular. X-ray rocking curve linewidth measurement shows a general reduction in the linewidth with increasing growth temperature and is insensitive to the substrate misorientation. Fine surface morphology revealed by Nomarski interference microscopy shows no correlation with x-ray linewidth. Results on the reduction of dislocation by varying growth temperature, substrate misorientation angle, and using AlGaAs/GaAs superlattice barriers for dislocation propagation are presented and their effectiveness are discussed. A realistic scheme to achieve an unwarped wafer with low dislocation density is proposed.

Properties of the two-dimensional electron gas in modulation-doped GaInAs(P)/InP structures grown by low-pressure metalorganic vapor-phase epitaxy

This paper is concerned with the characteristics of the two-dimensional electron gas (2DEG) at modulation-doped GaInAs/InP and GaInAsP/InP heterojunctions and GaInAs/InP single-quantum-well structures grown by low-pressure metalorganic vapor-phase epitaxy (LP-MOVPE) at 20 hPa. Using trimethyl-In, trimethyl-Ga, AsH3, and PH3 as source materials, this process permits the deposition of very uniform films with abrupt interfaces and doping profiles. We give the first detailed analysis of modulation-doped structures by classical Hall effect, Shubnikov–de Haas, and quantum Hall-effect measurements. Study of the scattering mechanisms of the 2DEG in modulation-doped GaInAs/InP and GaInAsP/InP structures reveals a small interface roughness and a low impurity content at the interfaces. Electron mobilities at 4.2 K up to 189 000 cm2/V s for a GaInAs/InP and 72 000 cm2/V s for a GaInAsP/InP heterojunction as well as values as high as 170 000 cm2/V s for a GaInAs/InP quantum well structure demonstrate the excellent control of the growth process and the quality of the material attainable by LP-MOVPE.

Metastable defect structures in elemental and compound semiconductors

Metastable defect structures exhibit structural transformations between different atomic configurations under specific conditions of measurement or device operation. These transformations produce local property changes which modify the role of the defect in the material's electrical and optical behavior. We summarize the observations of metastable defect structures in Si, GaAs and InP. The driving forces for the local transformations are based on strain, electrostatic interactions and covalent bond reconstruction. Examples of each are demonstrated using results on the M-center in InP, iron-acceptor pairs in silicon, and interstitial carbon associates in silicon. This understanding will be related to the influence of electronic and thermal stimuli on defect structure and the role of these structural transformations in known device instabilities.

Hydrogen passivation of shallow acceptors in p-type InP

Undoped GaInAs/zinc-doped InP structures grown by metal-organic chemical vapour deposition have been exposed to a RF hydrogen or deuterium plasma. Secondary ion mass spectrometry experiments show deuterium diffusion in both materials and the existence of a hydrogen-acceptor pairing effect in the p-type InP layer. After hydrogenation, the InP layer becomes highly resistive as a result of a strong passivation of acceptors by hydrogen. Hall effect and conductivity measurements performed on a lightly thermally reactivated InP layer indicate that the hole mobility is significantly higher than in the non-hydrogenated InP layer. This increase is attributed to a decrease of the ionised acceptor concentration under hydrogenation and is consistent with the existence of a pairing between the proton and the ionised acceptor giving rise to neutral Zn-H complexes. The relative thermal stability of Zn-H complexes in InP:Zn if compared to GaAs:Zn can be interpreted with the help of the microscopic model of these complexes, hydrogen being more tightly bonded to a phosphorus than to an arsenic atom.

Surface reactions of silane with oxidized InP and their application to the improvement of chemical vapor deposition grown, InP-based metal-insulator-semiconductor devices

The first stage of chemical vapor deposition of SiO2 from SiH4 and O2 on InP has been investigated. SiH4 is shown to interact only with an oxidized InP surface. It plays the part of an interface deoxidizing agent, restoring the covalent bonding of surface InP atoms. Oxygen originally bonded to InP becomes bonded to the silicon deposit in silica-like bonds. This phenomenon has been used as an in situ surface cleaning step in the processing of metal-insulator-semiconductor InP structures. It leads to a strong decrease of the hysteresis in capacitance-voltage curves, demonstrating improvement of the interface properties.

Magnetophonon resonance in n+n-n+ InP up to 40 T

Hot-electron magnetophoton resonances in micrometre size n+n-n+ InP structures are reported in crossed electric and magnetic fields in the temperature range from 110 to 230 K. The full series of quantum oscillation was studied up to the quantum number N=1 using pulsed high magnetic fields up to 40 T. The sign reversal of the oscillatory magnetoconductivity extrema from maxima to minima was observed with increasing electric field up to 3*104 V cm-1. The physical mechanism for the reversal of the extrema is interpreted in terms of the electric-field-induced inter-Landau level inelastic scattering of carriers by longitudinal optic phonons.

Charge-discharge dynamics of disorder induced gap state continuum at compound semiconductor-insulator interfaces

Based on the recently proposed disorder-induced gap state (DIGS) model for interface states, the charge-discharge dynamics of interface state continuum at insulator-semiconductor (I-S) interfaces are theoretically analyzed and compared with the experiments on InP and InGaAs MIS structures. The concept occupation boundary used in the analysis clarifies the physics involved and simplifies the simulation of complex processes. By assuming a particular type of DIGS distribution in energy and in space, the observed complex hysteresis behavior of dispersion of MIS capacitance in MIS C-V curves as well as the current drift behavior of MISFET's are completely reproduced on computer, offering a unified understanding of a wide variety of phenomena associated with I-S interfaces.

Ballistic transport in semiconductor alloys

The electronic structure of semiconductor compounds GaAs, InAs, and InP and alloys Ga0.5In0.5As, Ga0.7Al0.3As, and InP0.5As0.5, obtained in the coherent potential approximation, is used to calculate the group velocity and velocity relaxation time limited by longitudinal optical phonons, alloy disorder, and ionized impurities as a function of electron energy at 300 K. The nonparabolic nature of the band structure is found to severely limit the electron mean free path. With the types of interactions considered to date, the presence of L valleys does not limit the mean free path of electrons moving in the 〈100〉 direction. At 1018-cm−3 doping, electron-electron interactions reduce the mean free path by only 15% to 20%. InAs and GaInAs alloys offer advantages over all the other materials for devices with base widths greater than 500 Å; however, for thinner devices, ∼100 Å, no material is appreciably better than GaAs, the III-V compound currently under best control. The ballistic device-related properties of several II-VI systems compare favorably with the III-V alloys studied here. However, the II-VI compounds are less robust structural materials leading us to recommend the III-V compounds.

Anisotropic Ion Beam Assisted Etching of Optical Structures in GaAs and InP

ABSTRACTIon beam assisted etching (IBAE) was used to define submicron structures into GaAs/AlGaAs and InP/InGaAsP heterostructures. Etch rates in excess of I pm/minute were obtained after optimization of the etching process, allowing the fabrication of optoelectronic structures which require smooth, vertical sidewalls and depths of several microns. By altering the gas flow and the ion beam parameters, the same technique was used to pattern electron beam-written structures with lateral dimensions of less than 30 nm and aspect ratios in excess of 5:1 in GaAs.