InP Single Crystals Research Articles

Investigation of buried homojunctions in p-InP formed during sputter deposition of both indium tin oxide and indium oxide

Although it is apparent that direct current (dc) magnetron sputter deposition of indium tin oxide (ITO) leads to the formation of a buried homojunction in single crystal p-type InP, the actual mechanism of type conversion of the InP surface is not clear, nor is it immediately obvious how further improvements may be achieved. Previously, we have suggested that type conversion is caused by indiffusion of Sn during the ITO deposition process and additionally demonstrated that this effect is strengthened by the presence of hydrogen in the sputtering gas. Recently, however, efficiencies of almost 17% (Global) have been achieved for cells fabricated by sputter depositing In2O3(IO) alone, strongly suggesting that the Sn may not be an essential part of type conversion. In this work, a variety of electrical and optical techniques has been used to assess the changes at the ITO/InP and IO/InP interfaces. From these, it is concluded that several mechanisms, including passivation of acceptors by hydrogen and ‘‘sputter damage,’’ occur simultaneously. This analysis suggests several directions for further improvement of these devices.

Localized vibrational modes in proton and deuteron implanted GaP single crystals

Infrared absorption spectra of proton and deuteron implanted GaP single crystals reveal two hydrogen induced modes with frequencies of 1839 and 2204 cm −1 and six deuterium induced modes with frequencies of 1260, 1295, 1333, 1602, 1635 and 1670 cm −1. From a comparison of these mode frequencies with those reported for proton and deuteron implanted GaAs and InP single crystals it follows that vibrating defects with both GaH(D) and PH(D) bonds are formed. The number of vibrating centres is found to be proportional to the damage density.

Wafer fusion: A novel technique for optoelectronic device fabrication and monolithic integration

Centimeter-size single-crystal InP or GaAs wafers have been fused together entirely, face to face or side by side, after a heat treatment in a graphite/quartz reactor which can press the wafers together through differential thermal expansion. Diodes formed by fusing p- and n-type wafers showed normal current-voltage characteristics and light emission. Fusion between lattice-mismatched wafers (i.e., InP and GaAs) has also been demonstrated.

Interfacial Reactions Between Thin Films of Co and InP (100)

ABSTRACTThe interfacial reactions between thin films of Co and single crystal InP have been studied. The reaction between the Co and the InP substrate already start in the as-deposited state to form In and P rich compounds. During annealing at 250°C for 30 min., phase separation takes place. In addition to unreacted Co, we find Co rich compounds, a Co-P compound in contact with the substrate, and Co-In compound in contact with the metal layer. The general morphology appears to be stable up to 500°C. At higher temperatures (500–600°C) P is released from the substrate. CoP4, Co2P, CoIn2 and In were detected by X-ray diffraction. At this stage the reaction is no longer uniform.

Channeling lattice location of Se implanted into InP by RBS and PIXE

The lattice location of Se atoms implanted into InP was studied by simultaneous RBS (for detecting In) and PIXE (for detecting Se), using 2.5 MeV proton ions in the channeling mode. For InP single crystals, the 〈111〉 atomic row consists of alternate In and P atoms, while in the 〈110〉 direction there exist pure In and P atomic rows. Since the channeling half-angle is proportional to Z21/2, where Z2 is the average atomic number of the constituent atoms in the row, it is possible to determine the specific lattice location and the substitutional fraction of Se atoms in InP by measuring angular distributions of Se and In across the 〈111〉 and 〈110〉 axes. The results show that Se atoms occupy P sites with different fractions depending on the implantation temperature and dose.

Surface studies of AIIIB

Backscattering-energy spectra were measured for 2-MeV He ions channeled in 〈100〉 GaP, GaAs, and InP single crystals with natural oxide surface layers. The analysis of the experimental spectra was performed by the Monte Carlo simulation. The simulation program is based on the binary-collision model. The influence of the surrounding atoms and the energy loss of the channeled particles were taken into account. Also, different types of the ion-atom potential were tested. The simulated channeling spectra were calculated with respect to the random yield which makes it possible to fit experimental spectra without any normalization. Based on the simulation program, the thickness of the surface oxide layer, thermal vibration amplitudes of crystal atoms, and random stopping power of incident ions were determined. The values obtained were compared with the previously published theoretical and experimental data.

Photoluminescence studies of Si-implanted InP

Room-temperature integrated photoluminescence of Si-implanted n-type and semi-insulating wafers of single-crystal InP has been investigated as a technique for characterizing the quality of ion-implanted and annealed material. It was found that the intensity of the luminescence is a good indicator of the quality of the annealed samples. Using both rapid thermal annealing and conventional furnace annealing, not only was it possible to monitor the progressive activation of the implanted impurities, but we were also able to characterize the degradation occurring in the InP crystal due to the thermal exposure and to compare the results using different methods of surface protection. Combined with progressive wet etching of the implanted layers, it was also possible to use the photoluminescence response to spatially profile the activation and the degradation of the wafers. The results suggest that annealing, in general, is not able to restore the quality of the original unimplanted semiconductor and that even short transient anneal cycles can lead to detectable thermally induced material degradation, which extends many micrometers into the InP.

Electron-beam-induced dislocations in GaAs and InP single crystals

Dislocations have been induced in GaAs and InP single crystals by the electron beam exposure in a scanning electron microscope, with neither a mechanical bending nor a special pretreatment of the specimens. The generation and movement of the dislocations were not dependent upon the electron beam energy, crystal orientation, dopant nature, or doping level, but only on the electron beam current; a beam current of (1–2)×10−6 A was found to be the threshold for the dislocation release. By increasing the beam current up to 5×10−6 A, As or P losses from the specimen surface have been evidenced. In GaAs (001)-oriented crystals, the dislocations were found to be of pure edge type with the Burgers vector normal to the sample surface. A climb process, involving As or P vacancy migration, has been assumed to be the physical mechanism responsible for the dislocation origin.

Channeling and photoluminescence studies of heat-treated InP single crystals

2 MeV α-particle channeling and photoluminescence investigations were carried out to study the effects of heat treatment on 〈100〉 InP single crystals heated in powdered InP or Sn-InP melt ambients at 500–550 ° C for various durations. Observations suggest two types of native defects: type I defects which quench luminescence and increase in concentration in a phosphorus-deficient environment, and type II defects which are responsible for changes in the minimum channeling yield. These latter type defects multiply during short annealing cycles, but reduce in concentration in the longer annealing cycles in both powdered InP and Sn-InP melt ambients.

Convergence of the incident beam in reflection Electron Microscopy

The RHEED (Reflection High Energy Electron Diffraction) patterns as essential indications of the diffraction conditions in relation to REM (Reflection Electron Microscopy) imaging provide a wealth of information about the surfaces. They contain extensive patterns of Kikuchi lines, bands and envelopes resulting from diffuse inelastic scattering processes. They also contain arrays of diffuse spots forbidden by the boundary conditions for elastic scattering but generated by multiple diffuse scattering processes.However, a word of caution has to be sounded. Strictly speaking, the normal RHEED pattern does not exactly present the diffraction condition for REM imaging in a commercial transmission electron microscope. Practical and theoretical studies of the electron optics of the illuminating system on a Philip-400T transmission electron microscope, in which the specimen is immersed in the magnetic field of the twin objective lens, indicate that the convergent angle of the incident electron beam can be adjusted precisely, in a range from about 0.1 mrad to 5 mrad, with a selection of the second condenser aperture size, by adjusting the excitation current in the second condenser lens. For the best contrast and illumination, the RHEED pattern is generally obtained by focusing the electron beam on the surface with the maximum convergence angle, and the REM image is obtained with an almost parallel illumination with the minimum convergence angle. A typical example obtained from a fresh cleavage (110) surface of InP single crystal is demonstrated in figure 1, in which (a) and (b) are RHEED patterns with the (10,10,0) specular Bragg-reflection condition fulfilled and correspond to the incident electron beam with 2 mrad and 0.2 mrad convergence angles, respectively; (c) is a REM image obtained under exactly the same operation condition as (b) except for changing from diffraction mode to image mode, which indeed has nothing to do with the illumination condition above the specimen position; and (c) is taken from an area consisting of many steps of atomic height. Comparison of (a) and (b) shows that, for the parallel electron illumination, only those diffraction spots are dominant which represent the possible diffracted directions and mark the intersections of Ewald sphere with reciprocal lattice rods of the crystal surface. The extensive Kikuchi lines, bands and envelopes, and even the parabolas appearing in (a), are scarcely visible in (b). This suggests that the channeling effects characterized as the appearance of surface diffraction parabolas showing in RHEED pattern are mainly caused by the portion of electrons with incident direction slightly deviated from the rows of atoms; that is, the inelastically scattered electrons propagating in the directions of rows of atoms only occur when the initial incident electrons interact with the lattice in a direction slightly different from that of the rows of atoms. Following this argument, we may propose that the contrasts observed in REM image are mostly contributed from the diffraction and phase contrasts.

Formation of buried high-resistivity layers in InP crystals by MeV nitrogen ion implantation

We have studied the formation of buried high-resistivity layers in InP single crystals by MeV ion implantation. It was found that the implantation of MeV nitrogen ions plus subsequent thermal annealing can generate a deep burried layer with resistivity up to about 10 6 Ω cm in n-type InP crystals. This layer has exhibited implant dose dependence, high thermal stability and reproducibility over a dose range of 5 × 10 14 −1 × 10 16 cm −2. The mechanism of insulating layer generation by implanation, based on cross sectional transmission electron microscopy (XTEM) and I– V curve measurements, as well as the application of this technique in device fabrication, will be discussed.

A comparative study of swelling, strain and radiation damage of high-energy proton-bombarded GaAs, GaP, InP, Si and Ge single crystals

Swelling is studied on GaAs, GaP, InP, Si and Ge implanted with 0.3 and 1.2 MeV protons in the range of fluences D = 10 15-8 × 10 17c m −2, for several proton energies, implantation and annealing temperatures ( T = 300–650 K). Within t the “buried” damaged layer all materials exhibit a volume dilation whereas in the near-surface layer only GaAs, GaP and Ge show considerable expansion and InP contracts due to the proton bombardment. For the interpretation of the results additional measurements of strain and damage density are taken into consideration.

Improvements in the organometallic heteroepitaxy of indium phosphide directly on silicon

Specular single-crystal InP epilayers have been grown directly on Si(100) substrates by low-pressure organometallic vapor phase epitaxy. The effects of the initial nucleation process on the structure properties of the films were investigated, and improvements in the growth technique leading to higher quality InP films are reported. The InP/Si epilayer grown under optimum conditions exhibits high optical quality compared with that of the InP homoepilayer. Post-growth thermal annealing at 780 °C was also confirmed to be effective in improving the overall quality of InP-on-Si. The results presented are superior to those reported previously for InP/Si heteroepitaxy.

Growth of InP on Si substrates by molecular beam epitaxy

The growth of single-crystal InP films on (100) Si substrates by molecular beam epitaxy (MBE) is described. Three different buffer layers were grown by gas-source MBE in order to reduce the density of dislocations created by the 8% InP-Si lattice mismatch. Double-crystal x-ray diffraction revealed that all buffer layers produced large-area single-crystal (100) InP films with the InP lattice tilted towards the 〈100〉 Si directions. A buffer layer of four Inx Ga1−x P/Iny Ga1−y P strained superlattices produced a specular InP film with an estimated dislocation density of 108–109 cm−2 and a residual stress of less than 5×10−4.

The dynamic gradient freeze growth of InP

III-V bulk crystal growth in a low temperature gradient environment results in low defect levels and improved material homogeneity, important for optoelectronic devices and integrated circuit applications. In this report, the design of a novel, 23 zone, high pressure, vertical furnace for the dynamic gradient freeze (DGF) growth of InP is described, which allows one to establish the wide range of thermal profiles necessary to achieve a basic understanding of growth-property relationships. Undoped, 〈111〉 seeded, 50 mm diameter InP single crystals have been grown with dislocation densities in the range of 10 2–10 3/cm 2. The material was found to be n-type with 77 K carrier concentrations of 3×10 15/cm 3, and mobilities exceeding 38,000 cm 2/V·s at 77 K. These parameters are considerable improvements over conventional undoped LEC InP.

Growth and characterization of InP epilayers on ZnSehen;coated Si substrates by low-pressure metalorganic vapor phase epitaxy

Heteroepitaxial growth of InP on ZnSe-coated Si substrates by low-pressure metalorganic vapor phase epitaxy is reported for the first time. Single-crystal InP epilayers with specular surfaces can be obtained. The ZnSe buffer layer, which is evaporated onto the Si substrate in another furnace, is effective in reducing the magnitude of strain in the InP layer. The best room-temperature electron mobility of the undoped InP epilayer can reach 3100 cm2 /(V s) with a carrier concentration of 1.5×1015 cm−3 . It was found that the InP electron mobility is critically dependent on the ZnSe buffer-layer thickness. The efficient photoluminescence compared with that of InP homoepitaxy indicates that the InP heteroepilayer is of high optical quality.

ChemInform Abstract: Growth and Characterization of Large Size, High Quality, InP Single Crystals.

AbstractSingle‐crystal InP wafers grown by both the vertical gradient freeze (VGF) technique (described in detail) and the liquid encapsulated Czochralski (LEC) method are studied by transmission X‐ray topography, transmission cathodoluminescence, and defect revealing etching.

Mechanism for radiation resistance of InP solar cells

Photovoltaic properties of InP solar cells and defect behaviors of InP single crystals irradiated with 1-MeV electrons have been studied in order to clarify the superior radiation resistance of InP solar cells compared to Si and GaAs solar cells. It is confirmed that the excellent radiation tolerance of the InP cells is originated from the room-temperature annealing and minority-carrier injection-enhanced annealing phenomena of major radiation-induced defects in InP. The main defects in InP induced by irradiation at room temperature are thought to be due to a Frenkel pair of phosphorus vacancy and interstitial. They are much more mobile than those in GaAs.

Direct-current magnetron fabrication of indium tin oxide/InP solar cells

Interest in InP-based solar cells has recently been renewed due to the demonstration of excellent radiation resistance and the achievement of device efficiencies in excess of 20% (AM 1.5). Previous analysis of the indium tin oxide (ITO)/InP cell show it to be an extremely shallow homojunction which could, in principle, offer an even greater resistance to radiation than the deliberately grown organometallic chemical vapor deposition homojunctions. In this work, we have fabricated efficient solar cells of ITO/InP using dc magnetron deposition of the ITO into single-crystal InP substrates. The aim was to optimize the efficiency by varying the proximity of the substrate to the target and the input power to the plasma. Slight variations in efficiency have been observed but correlation with the fabrication parameters has been weak. Nevertheless, efficiencies over 16.5% have been achieved and verified at the Solar Energy Research Institute. This is the highest ever achieved for devices of this construction. Detailed studies of the annealing behavior of the cells have been made and interfacial changes observed using Raman spectroscopy and secondary ion mass spectroscopy. These observations, together with measurements of light and dark current/voltage, and quantum efficiency characteristics, have been used to model the behavior of the cells and explain their lack of sensitivity to the fabrication conditions.

Characterization of SrF 2 thin films and of SrF 2/InP structures

The composition of SrF 2 thin films deposited on carbon substrates by sublimation under vacuum has been investigated by Rutherford backscattering of α particles. It is shown that, for a substrate temperature T S = 573 K during the condensation of the vapour, the bulk composition of the layers is quasi-stoichiometric. Only a slight lack of fluorine, correlated with the presence of oxygen, is observed near their external surface. Coating with a very thin film of gold prevents air contamination. The interactions of such compounds with InP(100) single crystal have been deduced from X-ray diffraction and X-ray photoelectron spectroscopy studies. On the one hand, thin SrF 2 films have been found to be polycrystalline, a part of the polycrystals being oriented like the InP crystal, and, on the other hand, chemical bonds between phosphorus and fluorine have been observed at the insulator-semiconductor interface.