InP Samples Research Articles

Cross-sectional transmission electron microscopic study of Au/GaP and Au/InP contacts

Au(80 nm)/GaP(111) samples were heat treated in forming gas in the temperature range of 450–550 °C. Very thin elongated α-Au(Ga) grains were grown into the GaP at 475 °C as a result of the interface reaction between Au and GaP. A surface (interface) energy driven grain growth in Au-Ga solid solution was observed after annealing at 500 °C. At 525 °C long, flat grains were formed from the thin elongated ones of α-Au(Ga). At 550 °C the metallization melted due to its high Ga content. During the solidification the shape of drops was preserved, and the metallization consisted of Au2Ga and Au7Ga2 grains. Au(100 nm)/InP(111) samples were annealed at 375 and 400 °C in forming gas for 10 min. Elongated crystals grown into the InP substrate due to the interaction between gold and InP were observed. Au9In4 grains are situated in these pits in the matrix of the Au2P3 monoclinic phase.

Infrared absorption of n- and p-type Fe-doped InP and mapping of the Fe distribution

The near-IR absorption spectra of n- and p-type Fe-doped InP were measured at room temperature in a wide range of Fe concentrations. A clear correlation was found between the Fe content in the InP samples which were only Fe-doped and the optical IR absorption. The absorption coefficient at 1000 nm depends linearly on the chemical Fe concentration. The same dependence was observed for Te/Fe (n-type) as well as for Zn/Fe (p-type) co-doped InP. This effect is used for a quantitative evaluation of the Fe distribution across whole wafers (mapping). The results are compared to those of other characterization techniques, e.g. selective etching, showing an excellent agreement.

Amorphization of elemental and compound semiconductors upon ion implantation

Cross-sectional TEM studies of ion implantation induced amorphization in a large number of semiconductors have been performed. Samples of Si, AlAs, GaAs, GaP, GaSb, InP, InAs, and ZnSe were simultaneously implanted at 77 K with 20 keV Si+ at doses between 1 × 1014/cm2 and 1 × 1016/cm2. A dose of 1 × 1015/cm2 minimized the ion beam induced epitaxial crystallization and sputtering effects. The depth of the amorphous layer at this dose was compared with Monte Carlo damage density distribution calculations (TRIM'90). The threshold damage density (TDD) necessary for amorphization was determined for each compound. The values of the threshold damage density vary from as low as 2.4 × 1019 keV/cm3 for InAs up to 7.3 × 1020 keV/cm3 for AlAs. ZnSe never became amorphous and GaSb exhibited an unusual disordering after the highest dose. The values of the threshold damage density for the various compositions were compared with known thermochemical data and several bond energy estimates. No single calculation explained all of the trends observed.

Excitonic fine structure in the charge-transfer spectra of GaP:Fe.

Calorimetric-absorption spectroscopy at $^{3}\mathrm{He}$ temperatures reveals fine structure in the absorption spectra of Fe-doped GaP. A series of sharp lines is observed near 0.83 eV at the onset of the ${\mathrm{Fe}}^{3+}$\ensuremath{\rightarrow}${\mathrm{Fe}}^{2+}$ charge-transfer transition resembling a fine structure previously observed in the spectra of Fe-doped InP samples. In both cases, absorption lines are related to the formation of bound excitonic states in the ${\mathrm{Fe}}^{3+}$\ensuremath{\rightarrow}${\mathrm{Fe}}^{2+}$ charge-transfer transition. The present data indicate that the formation of such bound electron-hole states in the charge-transfer spectra of deep-level impurities is a common phenomenon in III-V semiconductors.

Cadmium segregation in LEC-grown InP

The results of electrical measurements and chemical analysis carried out on a number of Cd-doped InP samples are reported. The critical evaluation of the experimental data gives the segregation coefficient of Cd along with an estimate of its electrical activity.

X-ray photoelectron spectroscopy/Ar+ ion profile study of thin oxide layers on InP

The effect of incremental ion bombardment on the surface layers of an aqua regia etched InP sample was studied by monitoring the components of the In 3d5/2 and O 1s x-ray photoelectron spectroscopy (XPS) lines as the sample was bombarded with low energy (1 keV) Ar+ ions. The changes in the stoichiometry of the surface produced large shifts in the position of the In 3d and O 1s lines that were not paralleled by shifts in the P 2p line. Analysis of these shifts indicated that the surface was covered with a mixture of indium hydroxide and indium phosphate, with the phosphate closer to the InP substrate. It is proposed that this layer structure is due to differences in the dissolution rates of the oxidation products in the acid etch and the effect of the distilled water rinse. It may be possible to alter the composition of such oxides by carefully tailoring the etch conditions to optimize the kinetics for the particular oxide phase required. The analysis of the XPS lines also showed that the InP substrate was damaged at very low ion doses, and finally decomposed by the ion beam. When the ion ‘‘cleaned’’ sample was exposed to oxygen, a different oxide system was produced which consisted largely of In2O3 and InPO4 [or In(PO3 )x]. This model of the oxidized surface of InP is consistent with other measurements and we conclude that ion milling together with XPS and careful curve fitting can be used to find the nature of the thin oxides on InP.

Sputter-initiated resonance ionization spectroscopy: A matrix-independent sub-parts-per-billion sensitive technique applied to diffusion studies in SiO2–InP interfaces

Sputter-initiated resonance ionization spectroscopy (SIRIS) is a very selective and extremely sensitive technique to analyze semiconductor materials. In the SIRIS technique, the abundant neutral atoms released by the sputtering process are ionized by precisely tuned laser beams and counted in a mass spectrometer. The resonance ionization spectroscopy (RIS) process virtually eliminates isobaric and other interferences and reduces matrix effects dramatically. Depth profiles of Si and In were measured in unannealed and rapid-thermal annealed SiO2–InP samples using the SIRIS and secondary ion mass spectrometry (SIMS) techniques. The results show diffusion process of In through the SiO2 layer and of Si into the InP substrate, as well as the matrix independence of the SIRIS technique. A detection limit, defined as 2 standard deviation above background, of In in Si was measured at 300 parts per trillion (ppt) with a 0.75 μA, 0.8 μs wide ion beam pulse and less than 3 min analysis time at 30 Hz repetition rate. Therefore, a detection limit in the low ppt range could be achieved with a 5 μA ion beam current and 25 min analysis time.

Electron cyclotron resonance plasma etching of InP in CH4/H2/Ar

Plasma etching of InP in a microwave (2.45 GHz) electron cyclotron resonance (ECR) CH4/H2/Ar discharge has been investigated as a function of additional radio frequency (rf, 13.56 MHz) self-biasing of the sample. The etch rate of InP in a 1 mTorr, 250 W CH4/H2/Ar (5/15/7) ECR discharge increases linearly with applied rf bias, from 50 Å min−1 at 0 V to 350 Å min−1 at 200 V. Etching under ECR conditions alone yields smooth surface morphologies, while additional rf biasing of the discharge leads to In droplets remaining on the surface. This appears to be a result of preferential removal of P by the high atomic hydrogen density in the discharge. The room-temperature photoluminescence intensity from InP is reduced by approximately an order of magnitude after ECR etching, but is restored after removal of ∼20 Å from the surface by wet chemical etching. Gold Schottky contacts on InP samples etched under ECR conditions only yield barrier heights of 0.48 eV and ideality factors of 1.1, essentially identical to those on wet-etched control samples. ECR etching performed with an additional 100 V rf bias yields diodes with barrier heights of 0.44 eV and ideality factors of 1.6. Removal of ∼20 Å of the surface on these samples restores the values to those obtained on the control material.

Residual acceptor impurities in undoped high-purity InP grown by metalorganic chemical vapor deposition

Zn and an unidentified acceptor species, labeled A1, are the only residual acceptors that have been observed in a wide variety of undoped high-purity InP samples grown by metalorganic chemical vapor deposition. Carbon is not incorporated at detectable concentrations as a residual acceptor in metalorganic chemical vapor deposited InP. However, the longitudinal and transverse optical phonon replicas of the free-exciton recombination occur at the same energy as the donor/conduction band-to-acceptor peaks for C acceptors in low-temperature photoluminescence spectra. Since these replicas are usually present in photoluminescence spectra measured under moderate or high optical excitation, care must be exercised so that these peaks are not misinterpreted as C-related transitions.

Electrical and optical properties of rare earth dopants (Yb, Er) in n-type III-V (InP) semiconductors

Rare earths (REs) diluted into MBE grown and synthesised n-type InP samples create an acceptor-like level (at 30 meV for Yb and 60 meV for Er) below the conduction band; the activation energies are deduced from temperature dependent Hall effect measurements. From EPR experiments where the authors observe resonance due to the Yb3+ ground state in n-type samples, they deduce that this acceptor-like level is not the Yb2+/Yb3+ acceptor level. They propose that the RE creates an attractive potential for electrons in III-V semiconductors. They discuss the consequences of this property for the luminescence excitation mechanism of the luminescence.

Angle resolved X-ray photoemission study of rapid thermal annealing applied to different GaAs and InP samples

The crystalline order and itoechiomctry of the near surface of GaAs and InP substrates after rapid thermal annealing using a silicon wafer as a protecting cap have been deduced from angle resolved X-ray photo-emission measurements. A monolayer of As or P appears to be enough to prevent further material decomposition. For implanted samples (up to 1014/cm2 Si), the crystalline order is restored after the rapid anneal (without any important stoechiometry modification).

Phonon scattering studies of Ni and V centres in GaP and InP

Thermal conductivity measurements have been made from 50 mK to 100 K of GaP and InP samples doped with Ni or V. The GaP samples both show strong resonant phonon scattering at 500 and 380 GHz respectively which is attributed to the T1-T2 tunnelling splitting associated with a dynamic orthorhombic Jahn-Teller distortion of the T1 orbital ground state of Ni2+ and V2+. Low-frequency scattering in both systems is tentatively attributed to these same ions in complex with a defect. The assignment of the scattering to V2+ is supported by studies of photo-induced changes in the V2+ concentration. Uniaxial stress measurements on GaP:V suggest strong coupling to E modes but the strength of the coupling to T2 modes is less clear. The absence of resonance scattering in a n-type sample of InP:Ni suggests the Ni is all in the Ni+ state (2T2) as expected and the absence of scattering in n-type InP:V is consistent with the instability of V2+ in that system.

Picosecond photorefractive response of GaAs:EL2, InP:Fe, and CdTe:V

Measurements and theoretical calculations are presented for the photorefractive effect in three semi-insulating semiconductors (GaAs:EL2, InP:Fe, and CdTe:V) using 29-psec pulses at a wavelength of 1.06 microm. The photorefractive gain is largest in the CdTe crystal and smallest in our InP sample. The major differences between the materials responsible for this are the electro-optic coefficients, the mobilities, the absorption coefficients, and the amount of electron-hole competition.

Charge-transfer kinetics at an indium phosphide semiconductor electrode: Hole injection process in the presence of the Ce 4+/Ce 3+ couple

Electrochemical and electroluminescence measurements using rotating disk (n- and p-type InP) electrodes have been used to prove that the mechanism of the reduction of Ce 4+ ions occurs by a pure hole injection process in the valence band. The holes injected into the valence band induce the corrosion of InP samples in the dark. During the dissolution electrons are injected into the conduction band from decomposition intermediates.

Surface accumulation of hydrogen during capless annealing of InP

InP samples, which had received a capless anneal in a phosphine/hydrogen atmosphere, were examined for hydrogen contamination by secondary-ion mass spectrometry. It is found that hydrogen accumulates at the InP surface during annealing. Annealing of Be-implanted InP leads to similar profile shapes for the Be and H atoms. Passivation of the Be acceptors, if effective at all, appears to be of only minor significance.

Far-infrared spectroscopic identification of D- states in GaAs, InP and InSb

D- states (i.e. the states formed by a neutral donor, D0, binding an extra electron), D0 interexcited state transitions (i.e. n to m where the principal quantum numbers n, m are greater than 1) and cyclotron resonance are all observed simultaneously in the far-infrared spectrum of n-GaAs and n-InP. This observation constitutes the first unambiguous identification of D- states in a compound semiconductor. D- states have been observed in seven GaAs and two InP samples. A chemical shift is observed, but no central cell splitting is found even at the largest available fields (i.e. 24 T). D- states are studied under a variety of experimental conditions such as hydrostatic pressure, temperature and electric field bias. The application of hydrostatic pressure strongly enhances the D- intensity in VPE InP, but not in VPE GaAs. Effects attributable to the formation of D- complexes occur in GaAs when the temperature is reduced to 2 K. The intensity of the D- transition increases markedly with increasing electric field bias. Divergence between theory and experiment is evident when the dimensionless magnetic field parameter, gamma , exceeds unity, indicating the inadequacy of existing variational calculations in this regime. D- triplet and singlet transitions are tentatively identified in n-InSb.

Study of Sb condensation on InP(100) substrates previously cleaned by low energy Ar + ion beam

Electron loss spectroscopy (EELS) and AES have been performed in order to investigate a (100) InP surface subjected to a controlled Sb deposition. The InP(100) surface was previously cleaned by Ar + ion bombardment at low energy leading to the removal of the impurities and the formation of some metallic indium. After Sb deposition, EELS reveals a new surface configuration. Heating of such surface decreases the roughness induced by In droplets; Sb appears strongly fixed with θ < 1 monolayer and gives a great stability to the InP(100) samples.

Study of Sb condensation on InP(100) substrates previously cleaned by low energy Ar + ion beam

Electron loss spectroscopy (EELS) and AES have been performed in order to investigate a (100) InP surface subjected to a controlled Sb deposition. The InP(100) surface was previously cleaned by Ar + ion bombardment at low energy leading to the removal of the impurities and the formation of some metallic indium. After Sb deposition, EELS reveals a new surface configuration. Heating of such surface decreases the roughness induced by In droplets; Sb appears strongly fixed with θ < 1 monolayer and gives a great stability to the InP(100) samples.

Characterization of high-energy heavy-ion implanted InP crystals by a variety of techniques

MeV ion implantation into InP compound semiconductor crystals with 5 MeV nitrogen ions has been investigated. The subsequent characterization was undertaken by a variety of techniques such as nuclear resonant reaction analysis, channeling Rutherford backscattering spectrometry, X-ray rocking curve measurement and cross-sectional transmission electron microscopy. These techniques have clearly revealed substantial changes in structural properties and radiation-induced damage distribution as well as the influence of post-implantation annealing in 15N ion-implanted InP samples. The results from these measurements, which are presented in this paper, are shown to be consistent with each other, and have led to a coherent description of the effects of the implantation and subsequent annealing. In a practical sense this has demonstrated the complementary nature of the analytical capabilities of all of these techniques used for the investigation of the processes involved in high-energy heavy- ion implantation.

Thermal and electric field induced defects in InP metal-insulator-semiconductor structures

The presence of deep levels in several samples of InP metal-insulator-semiconductor (MIS) structures was studied using the deep level transient spectroscopy technique. The InP MIS structures were fabricated using three different methods of oxide formation, two of which are chemical oxides and the third is plasma-grown oxide. Defect levels ranging from (Ec−0.22) to (Ec−0.6) eV were observed in the samples. However, the levels at about (Ec−0.22) and (Ec−0.35) eV were detected only after increasing the reverse-bias voltage to −2 V at a temperature of about 390 K. This phenomenon occurred in all the samples studied, irrespective of the method of oxidation. The appearance of the peaks corresponding to the shallower traps is irreversible and may explain the performance instability commonly encountered in InP MIS-based devices.