Masami Tatsumi

Micro-Raman Characterization of Starting Material for Traveling Liquidus Zone Growth Method

Bulk InxGa1-xAs is an excellent lattice-matched substrate material for InGaAs-based laser diodes. However, it is very difficult to grow compositionally homogeneous InxGa1-xAs single crystal. The growth of single crystal with homogeneous composition using the newly developed traveling liquidus zone (TLZ) growth method is expected. In the TLZ method, cylindrically shaped polycrystalline starting material with a graded compositional profile is the basic requirement. This paper presents some results of micro-Raman scattering studies of the compositional fraction in these starting materials. The compositions evaluated by Raman scattering in various InxGa1-xAs wafer-type samples show good agreement with those examined by the standard method of chemical analysis. Compositional profiles obtained from as-ground and polished surfaces have been compared to understand the necessity of surface polishing in our experiments. The results presented here demonstrate that micro-Raman scattering is one of the best non-destructive methods for analyzing the entire compositional range of InGaAs compound materials.

Low dislocation density Si-doped GaAs single crystal grown by the vapor-pressure-controlled Czochralski method

Si-doped GaAs substrates have been widely used for optical devices. Recently, as the device fabrication process has changed, larger diameter substrates can be used. Almost dislocation-free Si-doped GaAs crystals of 75 mm diameter, which are suitable for the fabrication of optical devices, have been successfully grown using our vapor-pressure-controlled Czochralski (VCZ) method. The generation of slip dislocations could be suppressed and the growth of the dislocation-free crystal was achieved by decreasing the thickness of B2O3. The VCZ crystals contained a large amount of unintentionally doped boron (B) of about 1018 cm−3. By comparing the electrical data of the VCZ crystals with those of the gradient freeze (GF) crystal free from B, it is found that B acceptors decrease the intrinsic compensation ratio ([SiAs][SiGa]).

Liquid-phase epitaxial growth of bismuth silicon oxide single-crystal film: a new optically activated optical switch.

A single-crystalline double-layered structure of a pure (80-microm)/doped (39-microm)/pure Bi(12)SiO(20) (BSO) substrate was grown for the first time by a new liquid-phase epitaxial growth to form an optical waveguide. The waveguide layer is BSO doped with CaCO(3) (0.1 wt. %) and Ga(2)O(3) (0.197 wt. %) and has a refractive index 0.07% higher than the substrate. The optical absorption coefficients were decreased by more than 1 order of magnitude by doping with the elements Ca and Ga. The high-sensitive photoconductivity of pure BSO was also reduced. Using these unique properties, we have constructed a new type of optically controlled planar optical switch.

Growth Of Low-Dislocation-Density InP Single Crystals By The VCZ Method

Low-dislocation-density InP single crystals have been successfully grown under the low axial temperature gradient of dT/dZ = 30°C/cm by the VCZ method, which is an LEC method with phosphorus vapor pressure applied over the liquid encapsulant during growth. The average EPD is about 2,000 cm-2 in the 2-inch diameter crystals doped with Fe or Sn. The slip-free and dislocation-free crystals have been obtained by doping S of 2 x 1018cm-3 at the seed end. The InP crystals have uniform distributions of electrical properties with variations of less than 2%. The photoluminescence measurements of Sn-doped crystal have revealed no deep level due to phosphorus vacancy. The VPE InGaAs layer grown on the S-doped VCZ substrate exhibits few propagated dislocations and a very low leak current.

Directional solidification of InxGa1−xAs

Abstract We have investigated a constitutional supercooling and segregation phenomena in In x Ga 1− x As crystals unidirectionally solidified in a vertical system. The constitutional supercooling generates characteristic fluctuations of composition along the growth direction and this can be explained by a free nucleation ahead from the growth interface. The macroscopic compositional profiles of the grown crystals suggest that a transport of solute is mainly dominated by the diffusion. Such a growth mode is partly attributed to the difference in density between InAs and GaAs.

Electric-field-enhanced electron capture coefficient of EL2 level in semi-insulating GaAs

The electric-field dependence of electron capture coefficient to EL2 donor level in semi-insulating GaAs has been quantitatively determined from the analysis of the sublinear J–E characteristics up to 1150V∕cm before the onset of the low-frequency current oscillation. The three-probe guard-ring method was employed to obtain precise J–E characteristics. By considering the rate equation of the capture and emission process in the steady state, a simplified formula was derived to determine the electric-field dependence of capture coefficient. Our results agree well with those calculated from the multiphonon emission capture model.

The effect of gravity on crystal growth of InGaAs by the Bridgman method

Abstract InGaAs crystals were grown by the Bridgman method on earth and in microgravity. The difference of Ga composition profiles in the growth crystals is associated with the difference of heat transfer.

Chapter 5 InP Substrates: Production and Quality Control

Publisher Summary This chapter presents a discussion on the production and quality control of indium phosphide (InP) substrates. It describes the techniques related to InP single crystal materials and their characterization. The applications of InP crystals and the requirements for their quality is described in the chapter. The chapter reviews the details of crystal growth techniques, including recent developments obtained in laboratories. The techniques used in the evaluation, quality control, and wafer processing are also described in the chapter. InP single crystals have been used exclusively as conductive substrates for infrared optical devices. They are also under development as semi-insulating substrates usable in higher frequency microwave devices, such as metal–insulator–semiconductor field-effect transistor (MISFETs) and optoelectronic integrated circuits. There is a great demand for the development of higher quality indium phosphide single crystals. For this purpose, the technologies reviewed in the chapter, especially those concerning both the crystal growth and the processing of this material, are very important for future developments. Etch-pit density (EPD) is one of the best indicators of the quality of II–-V semiconductor crystals.

High-electric-field current–voltage characteristics and low-frequency oscillations in a low-dislocation-density semi-insulating GaAs

High-electric-field current–voltage (I–V) characteristics and low-frequency oscillations (LFO) have been measured in a low-dislocation-density semi-insulating GaAs. At the electrodes where several dislocations exist, the sublinear I–V behavior is weaker and more scattered, and the onset voltage of LFO is lower and its waveform is more complicated than those at the electrodes where no dislocations exist. The high-electric-field properties are discussed by the electrical inhomogeneities induced by the dislocations.

Influence of dislocation on high-electric-field property in semi-insulating GaAs

High-electric-field properties such as sub-linear I-V characteristic and low-frequency oscillations (LFOs) have been measured in a low-dislocation-density semi-insulating GaAs crystal. It is found that the sub-linear I-V behaviours and LFO waveforms measured at the cathodes where no dislocations exist are very stable but those measured at the cathodes where several dislocations are observed are not stable but more complicated, which is confirmed from Fourier-transform spectra of LFOs. It is explained that the high-electric-field properties observed here depend on the electrical inhomogeneities induced by the dislocations.