Indium Phosphide Crystals Research Articles

The Production of High Quality, III-V Compound Semiconductor Crystals

A new technique, called the Gault process, has been developed at AT&T Engineering Research Center for growing large, single crystals of gallium arsenide, gallium phosphide, and indium phosphide. It can produce seeded, 50-mm diameter crystals that have lower dislocation densities and more uniform properties at all levels of doping than crystals grown by existing methods. In this paper, we describe the Gault process, which is based on the vertical gradient freeze method. Its features include seeded crystal growth in a boron nitride crucible, with much lower axial and radial thermal gradients than the conventional, liquid-encapsulated Czochralski process. We show that establishing an appropriate phosphorus or arsenic vapor pressure over the melt is an effective method of stoichiometry control. Also, a nearly planar liquid-solid interface has positive implications for radial uniformity and the occurrence of twinning and polycrystalline nucleation.

Defects in LEC‐grown Indium Phosphide Crystals Doped with Tin

AbstractCrystalline defects in Sn‐doped LEC indium phosphide have been revealed by chemical etching and analyzed by TEM. Grown‐in dislocations, various kinds of defect clusters and colonies of microdefects were found. The symmetrical defect clusters are shown to equate mostly with larger dislocation loops exhibiting shear components and/or other dislocation arrangements generated by a stress source which is positioned in the centre of the dislocation cluster. Those centres are often formed by a plate‐like agglomeration composited of tiny inclusions and very small faulted dislocation loops. Such planarly arranged accumulations of microdefects lie on {111} planes. The direct vicinity of single threading grown‐in dislocations is always enriched with tiny perfect dislocation loops and precipitates. Additionally, very large isolated interstitial‐type perfect dislocation loops with b = a0/2 〈110〉 have been found by TEM experiments. Mostly, the {110} habit plane of such loops is decorated with an high number of small dislocation loops and precipitates as a consequence of dislocation climb.

A novel application of the vertical gradient freeze method to the growth of high quality III–V crystals

Large state-of-the art quality single crystals of gallium arsenide, gallium phosphide, and indium phosphide have been grown using a new process based on the vertical gradient freeze method. Seeded 50 mm diameter crystals are produced, at all levels of doping, which have lower dislocation densities than crystals grown by alternative methods. This is the first report of large diameter, low doped, ultra-low defect density InP. The radial uniformity is exceptional in these 750 gram 〈111〉 seeded InP crystals. The dislocation density of silicon-doped 〈100〉 GaAs grown by this method is less than 300/cm 2 without requiring high dopant levels. Undoped semi-insulating GaAs is stable with respect to thermal type-conversion. The results in GaP compare favorably with the reported state-of-the-art LEC crystals. The process features growth in a boron nitride seeded crucible, with axial and radial thermal gradients that are much lower than in the conventional LEC process. The establishment of an appropriate phosphorus or arsenic vapor pressure over the melt is shown to be an effective method of stoichiometry control. The process details are explained for the growth of GaP and some InP and GaAs results are presented. The equipment used in the growth apparatus, as well as the growth sequence and process control strategies, are described. The impact of the design of the hot zone elements on the shape of the liquid-solid interface is discussed. The establishment of a near planar liquid-solid interface has positive implications for radial uniformity and the occurrence of twinning and polycrystalline nucleation.

InP crystal growth on planar SiO2 substrates

Orientation-controlled InP microcrystals are grown on planar SiO2 substrates by reacting molten In thin films with vaporized phosphorus in a closed system. Indium phosphide crystals having a (111) texture of about 7 μm in size, grow at the periphery of the In islands when the substrate is heated at 500 °C under a phosphorus vaporizing temperature of 330 °C. When the In thin films are triangularly patterned, the in-plane 〈110〉 crystal direction is aligned parallel to the pattern edges by the capillary force effect between the In liquid and InP crystal.

The identification of precipitates in v-doped InP single crystals

Abstract Precipitates which form in vanadium-doped single crystals of indium phosphide during LEC growth are shown to be the hexagonal phase, vanadium monophosphide.

Electron and iron concentration in semi-insulating indium phosphide

Three iron-doped semi-insulating indium phosphide crystals have been grown by the liquid encapsulated Czochralski technique. Measurement of the iron concentration along the crystal by secondary ion mass spectroscopy establishes an effective distribution coefficient for Fe in InP of (5±3)×10 −4

Anisotropic undercutting in (100) indium phosphide

We present the undercutting rate of an indium phosphide crystal as a function of angle within the (100) plane. We use concentrated HC1 as the etchant and epitaxial InGaAsP as an etch mask. Undercutting behaviour including wall profile is determined as a function of etch time. The resulting description can be used to design crystallographic structures with a variety of orientations.

The single crystal growth and electrical properties of cobalt-doped indium phosphide

It is shown that semi-insulating properties can be induced in single crystals of indium phosphide grown by the liquid encapsulation Czochralski technique by using cobalt as a dopant. A mean value of segregation coefficient for cobalt in InP equal to 4 × 10−5 has been determined. Precipitation of a phosphide of cobalt is shown to limit the yield of useful semi-insulating material at high cobalt concentrations. The onset of semi-insulating behaviour occurs at a cobalt concentration in the crystal which equates approximately to the residual background concentration of n-type carriers. The close analogy of this behaviour with that observed in iron-doped crystals suggests that the semi-insulating properties are derived from Co2+ energy states which are shown to be present in these cobalt-doped crystals.

The identification of faulted prismatic dislocation loops in single crystals of undoped InP

High-voltage transmission electron microscopy has shown that undoped single crystals of indium phosphide, grown by the liquid-encapsulated Czochralski technique, can contain linear arrays of faulted dislocation loops. The plane of the loops is (1 1 0), the fault vector is 1/n [1 1 0] and the Burgers vector of the dislocation loop is 1/n [1 1 0]. A direct correlation has been obtained between these loops and arrays of both ridge and prism features revealed by chemical etching. Sequential use of two etchants has also established a direct link between the faulted dislocation loops and the slip dislocations induced by thermal stresses during crystal growth. A study of a number of crystals grown from differently prepared starting materials suggests that the formation of the loops is associated with departures from stoichiometry and inhibited by the presence of dopant impurities.

Growth of large indium phosphide crystals

Indium phosphide crystals up to 80 mm diameter and up to 3 kg weight have been grown by the liquid encapsulated Czochralski method, with boric oxide as encapsulant. Polycrystalline indium phosphide was first synthesized by direct reaction between the elements in graphite or pyrolytic boron nitride tubes, enclosed in sealed quartz ampoules. This gives dense polycrystalline ingots in high yield with only a slight amount of free indium. This material is used in the LEC process. Undoped crystals are n-type with carrier concentration of 5 × 10 15 to 1 × 10 16 cm -3. The dominant shallow donor impurities are sulphur and silicon. n-Type crystals have been grown using tin or tellurium as dopants, with carrier concentration up to 4 × 10 18 cm -3, and zinc and cadmium dopants have been used to produce p-type material. Provided that the donor concentration is less than 5 × 10 16 cm -3, then iron doping yields semi-insulating material with a resistivity greater than 10 7 ohm cm, which is thermally stable under epitaxial growth conditions. Etch pit densities for large crystals fall in the range 2–5 × 10 4 cm -2 increasing along the crystal from seed to tail.

Influence of the surface on photoluminescence from indium phosphide crystals

The photoluminescence of indium phosphide has been measured on crystals in ultrahigh vacuum and subsequently oxidized in a controlled manner. The luminescence intensity can vary by more than an order of magnitude and shows a close correspondence to the known shift of the Fermi level at the surface under oxidation. We conclude that the oxidation-induced surface space charge layer is nonradiative due to the presence of the electric field. The band bending and surface charge variation can be estimated quantitatively from the data. The influence of surface contamination on Schottky barrier formation is also reported.

Deformation behaviour of single crystals of InP in uniaxial compression

The deformation characteristics of indium phosphide (InP) single crystals under uniaxial compression have been examined as a function of strain rate, temperature and orientation. It has been shown that at temperatures below 0.55Tm (Tm=melting point; 1335 K) the material fractures in a brittle manner whereas at higher temperatures, within the range 0.55 to 0.71Tm, plastic deformation occurs by both slip and deformation twinning; above 0.71Tm, slip alone is the operative deformation mechanism. The observed operative slip systems are of the type {1 1 1} 〈0 1 1〉 which are characteristic of most Group IIIb-Group Vb compounds. Deformation twinning occurs predominantly on {1 1 1} planes but some activity is also observed on planes of the type {3 4 5}.

Growth and characterization of SSD InP crystals used as substrates for infra‐red LED's

AbstractBulk indium phosphide crystals have been grown by the synthesis, solute diffusion (SSD) method. Various growth temperatures and temperature gradients in the indium melt were investigated. The growth temperature of about 850–900°C and the temperature gradient of about 10–15°C cm−1 were found as the most suitable growth conditions. All grown crystals were of the n‐type either undoped or doped with Te or Sn. Infrared light‐emitting junctions were grown by single LPE process. Characteristic surface structures of InP epitaxial layers as a function of the growth temperature and cooling rate were observed. Efficiencies of LED's have been typically 0.8%. Single LPE process on LEC InP substrates has given LED's with substantially lower efficiencies.

The influence of intermediate adsorbed layers on the metal contacts formed to indium phosphide crystals

A whole range of surface sensitive techniques have been applied to probe the nature of the contact formed between indium phosphide (110) surfaces and a range of metals. Contacts to atomically clean cleaved surfaces, and to ones contaminated in a controlled way with oxygen, air or chlorine have been studied. High exposures to these gases, prior to the deposition of the metal, have a drastic influence on the nature of the contact and the electronic properties of the interface appear to be dominated by chemical effects. The results are considered in terms of various theoretical pictures leading to the conclusion that the interfacial defect model is the most relevant for the systems under consideration here.

The interaction of chlorine with indium phosphide surfaces

The adsorption and reaction of chlorine with clean cleaved (110) faces of indium phosphide crystals has been investigated by a range of electron spectroscopic techniques. For low exposures the chlorine is relatively weakly bound but for high exposure reaction with the surface leads to corrosion, the removal of some phosphorus from the surface layers, and the creation of a disordered surface. Work functions and electron affinities have been established and the behaviour of Schottky barriers formed at metal-indium phosphide interfaces are discussed in the light of these findings.

Pure and doped indium phosphide by vapour phase epitaxy

The dependence of carrier concentration on molar fraction can be utilised in fabricating epitaxial multilayered structures for device manufacture, however the variation of the molar fraction of phosphorus tricholoride in the seed region during growth affects the growth rate and homogeneity of the layers as well as carrier concentration and these factors culminate in a poor yield of slices for device processing. Silicon has been indentified in this work as the natural molar fraction controlled impurity both by analysis and source doping experiments. Inadequate control of layer thickness and doping density has led to a detailed study of sulphur doped indium phosphide crystals. By this means epitaxial wafers of sulphur doped indium phosphide that exhibit identical concentration-depth profiles and offer equivalent device characteristics to their molar fraction controlled predecessors can now be grown with an improved reactor yield.

Concentrations of carbon and oxygen in indium phosphide and gallium arsenide crystals grown by the lec technique

The concentration of carbon and oxygen has been measured in various samples of LEC–grown InP and GaAs crystals using gamma photon activation analysis and mass spectrometry. The concentration of these elements was found to be extremely low (0.1–0.3 ppma) contrary to previouslyreported work.

Zone melting of indium phosphide

Bulk indium phosphide crystals have been prepared by zone melting with dislocation densities 104 ≤ Nd ≤ 105 cm-2. The residual impurity level in nominally undoped crystals and the dopant distribution in Cd-, Sn- and Ge-doped zone melted ingots, as revealed by spark source mass spectrometric analyses, indicate a strong interaction between segregation at the solid/liquid interface and vapor transport. The effective distribution coefficients for Sn and Ge in zone melted InP are ke(Sn) = 0.3 and ke(Ge) = 0.4. The free electron concentration measured in the middle section of nominally undoped ingots is ND-NA = 1.9 × 1015 cm-3 corresponding to a Hall mobility Μe = 3263 cm2V-1sec-l.

Liquid encapsulated czochralski pulling of InP crystals

The growth of bulk indium phosphide crystals via liquid encapsulated Czochralski pulling from both stoichiometric and nonstoichiometric melts is described. Nominally un-doped crystals with carrier concentration ND-NA = 6 × 1015 cm−3 and Hall mobilities of 4510 cm2/Vsec at room temperature were grown. Also, we prepared Zn-or Cd-doped p-type crystals in the range 1016 ≤ NA-ND ≤ 1018 cm−3 with Hall mobilities ≤ 130 cm2/Vsec and Sn-doped n-type crystals in the range 4 × 1017 ≤ NA-ND ≤ 1018 cm-3 with Hall mobilities ≤ 2400 cm2/Vsec. The dislocation density of LEC pulled InP crystals is typically ~ 104 cm−2.