Traveling Liquidus-zone Research Articles

High-Characteristic-Temperature 1.3-$\mu$m-Band Laser on an InGaAs Ternary Substrate Grown by the Traveling Liquidus-Zone Method

We have developed high-performance 1.3-mum-band laser diodes on an InGaAs ternary substrate with a low indium content (In:0.1) grown by a novel bulk crystal growth technique called the traveling liquidus-zone (TLZ) method. This laser has a long-wavelength lasing of 1.28 mum and provides lasing operation up to 195degC by using a highly strained InGaAs quantum well. The characteristic temperatures are 130 K from 25 to 95degC and 95 K from 95 to 155degC. We investigated junction heating by comparing the lasing wavelengths for pulsed and continuous-wave (CW) operation. And, we showed the possibility of realizing a high-performance laser on an InGaAs ternary substrate.

Convection Effects on Crystallinity in the Growth of In0.3Ga0.7 as Crystals by the Traveling Liquidus Zone Method

The influence of convection in a melt on the crystallinity of the TLZ-grown In(0.3)Ga(0.7)As crystals has been investigated by growing crystals with various shapes and dimensions on the ground. No single crystals have been grown when the crystal diameter was 10 mm, but we were successful in growing single crystals by reducing crystal diameter to 2 mm. These results suggested the importance of suppressing convection in the melt during alloy crystal growth because constitutional supercooling tends to occur at the freezing interface or ahead of the interface by the segregation effect. Large area is required for substrate use in various applications. This requirement can be fulfilled by the crystal growth in microgravity because density difference-induced convection is suppressed in microgravity. Another means for suppressing convection without deteriorating area is plate-shape crystal growth with reduced thickness. The latter can be applied on the ground and we succeeded in growing single crystals of plate-shaped In(0.3)Ga(0.7)As by the traveling liquidus zone (TLZ) method. Dimensions of obtained single crystals were 10 mm in width and 2 mm in thickness and lengths ranged from 20 to 40 mm. Compositional uniformity was good and 0.3 +/- 0.02 in InAs mole fraction was achieved.

Homogeneous SiGe crystals grown by using the traveling liquidus-zone method

It is indispensable to estimate a diffusion coefficient in a solution zone in order to grow a homogeneous crystal by using the traveling liquidus-zone (TLZ) method. To estimate the diffusion coefficient of Ge in the SiGe solution zone, result of a two-dimensional numerical simulation is compared with an experimental result. From the comparison, the diffusion coefficient is estimated to be 9.5×10 −5 cm 2/s. By using this coefficient, a sample translation rate for obtaining a homogeneous SiGe crystal is determined. By translating samples with appropriate rates, homogeneous Si 0.5Ge 0.5 crystals are successfully grown. The typical Ge composition is 0.496±0.006 for more than 13 mm long. The experimental result shows the homogeneity of ±1.2% in the mole fraction. This deviation corresponds to the variation of less than ±0.03% in the lattice constant. Since this variation is negligibly small, the homogeneity is excellent. Thus it is found that the TLZ method is the universal growth technique, which is applicable to the crystal growth of not only the III–V compounds but also the IV–IV compounds.

Excellent compositional homogeneity in In0.3Ga0.7As crystals grown by the traveling liquiduszone (TLZ) method

The influence of convection in a melt on the compositional homogeneity of the TLZ-grown In0.3Ga0.7As crystals has been investigated by growing crystals with various dimensions on the ground. Excellent compositional homogeneity such as 0.3 plus or minus 0.01 in InAs mole fraction for a distance of 25 mm was obtained when the melt diameter was limited to 2 mm and convective flow in the melt was suppressed. On the other hand, when the crystal diameter was increased to 10 mm, both axial and radial compositional homogeneity was deteriorated due to convection in the melt. Comparing with the numerical simulation, convective flow velocity less than 1.4 mm/h may be sufficient for growing homogeneous crystals and it is not so difficult to suppress convective flow velocity below 1.4 mm/h for 10 mm diameter crystals in microgravity. Therefore, larger homogeneous In0.3Ga0.7As crystals are expected to be grown by the TLZ method on board the International Space Station.

3420 飽和溶融帯移動法における二次元性低減に関する検討(S89-1 微小重力・宇宙環境利用(1),S89 微小重力・宇宙環境利用)

A one-dimensional theoretical model of the traveling liquidus-zone (TLZ) method gives a precise prediction of a growth rate. However, the one-dimensionality may be worse as a sample diameter increases. To investigate limit of one-dimensional approximation, a two-dimensional theoretical model of the TLZ method is introduced. By comparing the one-dimensional model and the two-dimensional one, two-dimensionality is defined. To calculate the two-dimensionality, numerical simulation is carried out. From the calculation result of the two-dimensionality in cases of various sample diameters, it is found that microgravity condition reduces the two-dimensionality since thermal convection is suppressed. However, the two-dimensionality is not negligibly small in the larger sample diameters. The reason of the residual two-dimensionality under the microgravity condition is investigated. From the numerical simulation, it is concluded that the residual two-dimensionality is caused by thermal conduction.

Latent heat effect on growth rate in the traveling liquidus-zone method

In order to obtain a homogeneous crystal by using the traveling liquidus-zone (TLZ) method, a conventional one-dimensional model is used to determine an appropriate sample translation rate. Although the conventional model predicts the appropriate translation rate, the latent heat effect is unknown since the conventional model is based on pure solution growth. Therefore, a new model including the latent heat is introduced to investigate the latent heat effect. By considering the new model, the maximum latent heat effect αmax is obtained. The αmax is negligibly small under the condition that the InAs mole fraction is far enough from 0 or 1 in the case of an InGaAs crystal. In order to estimate the actual latent heat effect α, one-dimensional numerical simulations with and without the latent heat are carried out. From the numerical results, the applicable limit of the TLZ method is discussed in the case of In0.3Ga0.7As crystals. The growth rate, which is regarded as a pure melt growth, is also discussed by extrapolating the α dependency.

Numerical analysis of growth rates in the traveling liquidus-zone method

One-dimensional numerical simulation is carried out in order to obtain growth rates at several temperature gradients. The simulation agrees well with experimentally obtained concentration profiles in solid. From numerical results, it is found that a growth rate is almost proportional to the temperature gradient in a low temperature-gradient region as the one-dimensional traveling liquidus-zone (TLZ) theoretical model predicts. However, the growth rate becomes slightly higher than the theoretically predicted one in high temperature-gradient region. On the other hand, the growth rate is almost proportional to solute concentration gradients in the whole range. These results indicate that the TLZ method is one of solution growth techniques. It is found that the TLZ method precisely predicts the spontaneous growth rate, within an error of 3% in the region of the low temperature-gradient.

Convection influence on mass transport in the traveling liquidus-zone method

The one-dimensional theoretical model of the traveling liquidus-zone (TLZ) method precisely predicts a sample translation rate for obtaining homogeneous crystals. However, no convection-related terms are included into the model. Here, convection influence on mass transport is numerically investigated. The numerical analysis shows that there are two vortices in the zone. In this case, the flow mainly enhances radial mass transport. In order to correctly understand the convection effect on the mass transport, a new index is introduced instead of the Sherwood number. The new index increases with the sample diameter. In the case of the sample diameter of 2 mm, the mass transport by convection is negligibly small as compared with that by diffusion. This is the main reason that the model prediction agrees well with the ground-based experimental results. In order to reduce the convection influence, microgravity condition is considered in the numerical analysis.

Convection influence on mass transport in the traveling liquidus-zone method

The one-dimensional theoretical model of the traveling liquidus-zone (TLZ) method precisely predicts a sample translation rate for obtaining homogeneous crystals. However, no convection-related terms are included into the model. Here, convection influence on mass transport is numerically investigated. The numerical analysis shows that there are two vortices in the zone. In this case, the flow mainly enhances radial mass transport. In order to correctly understand the convection effect on the mass transport, a new index is introduced instead of the Sherwood number. The new index increases with the sample diameter. In the case of the sample diameter of 2 mm, the mass transport by convection is negligibly small as compared with that by diffusion. This is the main reason that the model prediction agrees well with the ground-based experimental results. In order to reduce the convection influence, microgravity condition is considered in the numerical analysis.

A one-dimensional model to predict the growth conditions of In xGa 1− xAs alloy crystals grown by the traveling liquidus-zone method

The traveling liquidus-zone (TLZ) method has been used effectively to grow ternary alloy single crystals of uniform composition. In this study, a one-dimensional model is presented to predict the growth conditions of this technique. It was shown that under the assumed growth conditions, the model gives accurate predictions for the growth conditions of the TLZ method including the composition of the grown crystals. Numerical results agree with those of experiments.

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.