Crystal anomaly at the center of S doped InP wafers grown by the LEC method

Crystal quality of 2′ Φ S doped InP substrates grown by the conventional liquid encapsulated Czochralski method was studied by the photoluminescence mapping technique and double crystal x-ray diffraction method. Dark currents of InGaAs/InP PIN-photodiodes (PIN-PDs) fabricated on them showed the existence of an anomaly at the center of the substrate. Photoluminescence intensity abruptly decreased at the center of the substrate. An abnormal curvature of the lattice plane was found at the center of the substrate by the double crystal x-ray diffraction measurement. We discuss the correlation between crystal quality of the substrate and dark currents of PIN-PDs.     

Growth of low dislocation density InP single crystals by the phosphorus vapor controlled LEC method

Low dislocation density <100> InP single crystals have been grown by a phosphorus vapor controlled LEC method (PC-LEC). 3 inch S-doped and Fe-doped InP and 2 inch Sn-doped InP single crystals have been grown by this method. In S-doped crystals, the dislocation free area could be increased compared with that of conventional LEC crystals. 3 inch Fe-doped InP with the dislocation density lower than 10⁴ cm^?2 could also be grown. The average EPD was lower than 5×10³ cm^?2 in 2 inch Sn-doped InP. The photoluminescence intensity of PC-LEC crystals was much higher than that of conventional LEC crystals in the case of Sn-doped InP.     

Reduction of dislocation densities in InP single crystals by the LEC method using thermal baffles

We have developed a modified liquid encapsulated Czochralski (LEC) method with thermal baffles, by which low dislocation density InP crystals can be grown. In this method, thermal baffles are set on top of the crucible in order to suppress the gas convection and thus to improve the temperature gradient in the LEC furnace. However, the dislocation densities depend not only on the temperature gradient but also on other growth conditions, such as crystal/crucible rotation rates, cooling rates, and the thickness of the pBN crucible. Since the rotation rate affects the solid/liquid interface shape, it is an important factor for the reduction of dislocation densities. By optimizing these conditions, for Sn and Fe doped InP crystals, average dislocation densities less than 5 x 10³ cm⁻² can be achieved. Dislocation free (DF) S and Zn doped InP crystals can also be grown if the carrier concentration is more than 3 x 1018 cm⁻³. The DF crystals become rectangular in shape.     

Development of low-dislocation-density SI long 2-inch InP single crystals by the VCZ method

At Sumitomo Electric, 2-inch diameter 220mm-long semi-insulating InP single crystals with low dislocation density have been successfully developed by VCZ (Vapor pressure controlled Czochralski) method. This article describes the growth technique and characterization of low-dislocation-density semi-insulating long 2-inch InP single crystals.     

Fine structures of residual strain distribution in Fe-Doped lnP-100) wafers grown by the LEC and VCZ methods

By using a high-spatial-resolution scanning infrared polariscope, in-plane components of residual strain have been characterized quantitatively in 2′Φ wafers of Fe-doped InP( 100) single crystals grown by the liquid-encapsulated Czochralski (LEC) and the vapor pressure controlled Czochralski (VCZ) methods. The twodimensional distribution maps of LEC-grown wafers reveal characteristic fine structures such as slip-like patterns originated from crystallographic glides during the crystal growth process, highly strained spots and filaments due to inclusions or voids inside the wafer, or due to scratches on the surface. The sliplike patterns are seldom observed in the VCZ-grown wafers. The residual strain value averaged over the whole region of wafer is also examined, together with etch pit density and resistivity, as a function of the solidified fraction. It is found that the residual strain in the Fe-doped InP crystals grown by the LEC and VCZ methods mainly depends on the thermal stress during the growth process rather than on the impurity-hardening effect of Fe.Key words: InP, infrared polariscope, liquid-encapsulated Czochralski (LEC) method, residual strain, vapor pressure controlled Czochralski (VCZ) method     

Shallow donor impurities in InP bulk crystals grown by the synthesis, solute-diffusion technique

Far-infra-red photoconductivity measurements are used to study residual shallow donor species in InP bulk crystals grown by the synthesis, solute-diffusion technique. The observation of 1s-2p, m =+ 1 Zeeman transitions between the shallow donor-impurity states reveals that two dominant residual donors are included in the InP bulk crystals having carrier concentrations of less than 1 × 1015 cm?3 The donors are tentatively identified as Si and S.     

Field-effect transistors based on organic single crystals grown by an improved vapor phase method

High-quality organic single crystals are produced directly onto the substrates using an improved vapor phase method. Unlike the conventional vapor phase methods, the present method is characterized by forming a large-sized crystal to which semiconductor devices can readily be made. The relevant method requires small space of only a 10-cm cube in which a couple of plates are put in close proximity. The crystal growth is carried out nearly at the thermodynamic equilibrium within the narrow space surrounded with the two plates. Thin single crystals of several hundreds of micrometers in size are grown on one of those plates. For the organic materials to be crystallized, we have chosen 1,4-bis(5-phenylthiophen-2-yl)benzene (AC5) and 5,5-diphenyl-2,2′:5′,2″:5″,2:5,2-quinquethiophene (P5T) from among thiophene/phenylene co-oligomers. The resulting crystals are well-defined polygons, each side reflecting the specific crystallographic orientation. In particular, those grown on self-assembled monolayers are exceedingly flat and free from cracks. We have directly fabricated top-contact field-effect transistors on these crystals. The devices exhibit the excellent performance and keep it both in air and in vacuum for a maximum of a hundred days.     

Residual impurities and electrical properties of undoped LEC InAs single crystals

Impurities and their influence on the properties of InAs single crystals have been studied by combining the results of glow discharge mass spectrometry (GDMS), Hall measurements, Raman scattering and infrared absorption. The results indicate that carbon is a major impurity in LEC-InAs single crystals and exhibits a significant influence on the electrical and optical properties.     

非掺杂LEC-InAs单晶的残留杂质与电学性能研究

有关非掺InAs单晶中的施主杂质、缺陷及其产生规律的尚不清楚。本文利用辉光放电质谱（GDMS）定量分析了LEC法生长的InAs单晶的残留杂质,结合Hall测量、Raman散射和红外吸收等研究了施主杂质的来源和缺陷对材料性质的影响。     

High-resistivity GaSb bulk crystals grown by the vertical bridgman method

Heavily compensated GaSb (2-in.-diameter substrates) with resistivity as high as 7 × 10³ Ω-cm, corresponding to a net donor concentration of 3.5×10¹³ cm⁻³ at 77 K, and 16.4 Ω-cm, corresponding to net donor concentration of 1.16×10¹⁶ cm⁻³ at 300 K, have been obtained by tellurium (Te) compensation in vertical-Bridgman-grown bulk crystals. Very interesting p- to n-type as well as n- to p-type changes have been observed as a function of temperature in these samples.     

Optical spectra of Eu2+ ion doped KMgF3 single crystals grown by Bridgman method

High-quality KMgF3 single crystal containing 0.5 mol% europium (Eu) was prepared by an improved Bridgman method. X-ray diffraction (XRD), photoluminescence spectra and fluorescence lifetime were measured. The results indicate the reduction of Eu3+ to Eu2+ in the KMgF3 single crystal. Under the excitation of 259 nm, 370 nm and 394 nm, the sample has two distinct emissions of Eu2+:4f7→4f7(~363 nm) and 4f65d1→4f7 (~440 nm). The substitution site for Eu ion is confirmed. The optical property investigation result shows that the Eu2+ doped KMgF3 single crystal may be used as potential laser media and related materials for optical devices.     

Defects in CdTe single crystals grown by very fast vapor growth technique

Single crystals of CdTe were obtained by the very fast vapor growth technique. The four major defects, namely, multi-grains, lamellar, lateral, and micro-twins, which are fatal to the single crystallinity, were eliminated or limited by increasing the growth stability. This investigation indicates that the latent heat under high growth rate conditions should not be neglected. A model is developed to explain the effects of latent heat on the growth stability at the interface. A relationship between crystal morphologies and growth conditions was established. It strongly suggests that the above defects are growth stability related. The origin of twinning, dominated by growth stability, is discussed in this paper.     

Optical properties of Cr3+ doped Na5Lu9F32 single crystals grown by the Bridgman method

The growth of Na5Lu9F32 single crystals doped with Cr3+ ions in 0.1 mol%, 0.2 mol% and 0.5 mol% concentrations by Bridgman method was reported. The optical absorption and luminescence spectra decisively demonstrate that the Cr dopant enters Na5Lu9F32 as Cr3+. Fluorescence emission at wavelengths of 418 nm, 444 nm, 653 nm and 678 nm can be observed under the excitation of 372 nm and the fluorescence lifetime at 418 nm was measured to be ~10.31 μs. The possible crystal sites for Cr3+ ions in Na5Lu9F32 single crystal were discussed, and the lattice parameter Dq, Racach parameters B and C were estimated.     

Development of inclusion-free CdZnTe substrates from crystals grown by the vertical-gradient freeze method

With the aim of fabrication of (111) and (211) CdZnTe inclusion-free substrates for molecular-beam epitaxy (MBE) and liquid-phase epitaxy (LPE) growth of mercury cadmium telluride (MCT), we focused on fundamental research of the process of crystallization and cooling to room temperature. Based on the study of inclusion formation in dependence of Cd overpressure above the melt, an optimized process of crystal solidification was established. A key result of this study is the position of the Cd pressure, where inclusion-free crystals were fabricated without post-growth annealing. The crystals with a diameter of 100 mm and a height 40–50 mm were fabricated by the vertical-gradient freeze method (VGFM). The resulting ingots exhibit very good crystallographic quality, with a single-crystalline part filling 60–80% of the crystal volume. Substrates with orientation (111) and (211) and dimensions up to 4 × 4 cm were fabricated.     

Mechanical properties of pure and doped InP single crystals determined under local loading

The mechanical properties of pure and doped (Fe, Zn, Sn) InP single crystals have been investigated in the temperature range 293–600 K. It is shown that impurity hardening (increase in microhardness) is much more pronounced at high temperatures than at room temperature because of the retardation of moving dislocations by impurities, which is strongest at high temperatures. Appreciable scratch hardness anisotropy on the (001) face of the experimental crystals at 293 K was observed. It decreases rapidly as the temperature increases in the interval 293–600 K. It is shown that the [110] and directions on the (001) face of the experimental crystals are nonequivalent. The observed phenomena are explained by the different contributions of the two mechanisms of plastic deformation: slip and twinning in the process of scratch formation along the 〈100〉 and 〈110〉 directions, and along the [110] and directions. Fiz. Tekh. Poluprovodn. 31, 243–246 (February 1997)     

Thermomigration of tellurium precipitates in CdZnTe crystals grown by vertical bridgman method

Te precipitates in CdZnTe have been characterized by x-ray diffraction at room and higher temperatures. From the x-ray results at room temperature, it has been confirmed that Te precipitates in CdZnTe have the same structural phase as observed in elemental Te under high pressure. The x-ray results at higher temperature indicate that Te precipitates melt around 440°C. CdZnTe samples containing Te precipitates have been annealed at temperatures below and above 440°C with thermal gradient of ∼70°C/cm. Results of the observation with infrared microscope before and after the annealings indicate distinct occurrence of thermomigration of Te precipitates in samples annealed at temperature above 440°C compared with ones annealed at temperature below 440°C. Thermomigration velocity obtained from these results is ∼50 μm/h. The average value for the effective diffusion coefficient of the metallic atoms in Te precipitates calculated by using the thermomigration velocity is ∼3 x 10⁻⁵ cm²/s.     

Chemical polishing of CdZnTe substrates fabricated from crystals grown by the vertical-gradient freezing method

Chemical polishing is a process of crucial importance in the manufacture of epiready substrates for molecular beam epitaxy (MBE) of high-quality HgCdTe layers. With the aim of fabrication of (211) CdZnTe substrates, we focused on the fundamental research of polishing processes with respect to reducing subsurface damage. Wafers of the orientation (211) were prepared from the as-grown crystals by a process flow including oriented slicing, several steps of mechanical polishing, and finally chemical polishing. In the prechemical polishing process, several free and bound abrasives were applied to reach the surface roughness close to 1 nm. The surface polishing treatment included testing of the surface quality after each polishing step. We used an interferometer profiler, which yields detailed surface maps. Within chemical polishing processing, we have looked for an optimum composition of etchant based on the bromine-methanol/ethylene glycol solution and adequate polishing pad. We studied the substrate surface quality dependence on the rotation speed of the plate, sample loading weights, and duration of polishing. Correlation between the final surface roughness and layer thickness removed was established. The chemical polishing with a very low concentration of Br-methanol/ethylene glycol solution was found to yield very good CdZnTe surfaces with a perfect flatness.     

Low threshold 1.3 μm-GaInAsP/InP tensile strained single quantumwell lasers grown by low-pressure MOCVD

1.3 μm Ga_0.49In_0.51As_0.7P_0.3-1.15% tensile strained single quantum well (SQW) lasers are successfully fabricated. The lowest threshold current for a 200 μm-long, 20 μm-wide ridge waveguide laser with high reflectivity coating is as low as 6 mA, corresponding to a very low threshold current density of 150 A/cm²     

Growth of CdGeAs2 single crystals by the chemical vapor transport method

We have grown CdGeAs₂ single crystals by chemical vapor transport (CVT), a method not previously applied for this compound. The crystallographic data of this chalcopyrite (cell parametersa ₀ = 5.9456 ± 0.0001Å, c₀ = 11.2131 ± 0.0007Å) and its electrical transport properties are reported. Predominantly n-type crystals are obtained (at RTn = 1 · 10¹⁷cm?3, μⁿ = 2000 cm²(Vs)^?1). Vacuum heat treatment at 500° C yields a type conversion fromn- to p-type. In all p-type samples the minority carrier mobility is calculated to be larger than 10000 cm²(Vs)^?1.