Yukinaga Azuma

Growth of SiGe bulk crystal with uniform composition by directly controlling the growth temperature at the crystal–melt interface using in situ monitoring system

Abstract A SiGe bulk crystal with uniform composition was successfully fabricated by clarifying and controlling the growth parameters at the crystal–melt interface. An apparatus was developed for the direct in situ observation and precise control of the interface parameters such as the temperature and the position. The dynamical change of the growth rate of a SiGe bulk crystal in a temperature gradient can be known by utilizing the apparatus. The growing crystal was continuously pulled down at the pulling rate balanced to the growth rate to keep the interface temperature constant, which resulted in the excellent uniformity of the grown crystal. Our technique opened the possibility to incorporate multicomponent semiconductor substrates to the semiconductor heterostructure technology.

Compositional variation in Si-rich SiGe single crystals grown by multi-component zone melting method using Si seed and source crystals

The effect of the supply of depleted Si solute elements on the compositional variation in the Si-rich SiGe bulk crystals was studied using the method which was used to grow Ge-rich SiGe single crystals with a uniform composition. By selecting the proper pulling rate, we can obtain Si-rich Si1−xGex bulk crystals with uniform composition of x=0.1 without using the supply mechanism of depleted Si solute elements. When the supply mechanism of Si solute elements was used, the initial composition in Si-rich SiGe crystals can be much more easily determined by controlling the growth temperature than that in Ge-rich crystals because the Si seed crystal is not melted down. The supply of Si solute elements is very effective to change the compositional variation even for Si-rich SiGe crystals.

SiGe bulk crystal as a lattice-matched substrate to GaAs for solar cell applications

SiGe bulk crystal fabricated by a multicomponent zone-melting method was used as a substrate for epitaxial growth of GaAs. Compared with conventional GaAs/Ge heterostructure, the lattice mismatch of GaAs/Si0.022Ge0.978 was confirmed to be reduced by a decrease of the peak separation of (400) x-ray diffraction from the epitaxial GaAs layer and the substrate. Furthermore, the linewidth of the rocking curve of GaAs on SiGe was found to be narrower than that of GaAs on Ge. These results show that SiGe is promising material as an alternative substrate to Ge for realization of exactly lattice-matched GaAs/SiGe solar cells.

Growth of SixGe1-x (

A new growth system, which allows in situ monitoring of the crystal-solution interface, was developed and applied to grow SixGe1-x (x\fallingdotseq0.15) bulk crystal with uniform composition by the multicomponent zone-melting method. By utilizing the system, the dynamical change of the growth rate was evaluated from the nonlinear upward shift of the interface as a function of the growth time. Based on the monitoring, an attempt was made to balance the pulling rate of the ampoule with the growth rate of the crystal, which led to the suppression of the upward shift of the growth interface. Consequently, the compositional uniformity of the crystal in the growth direction was markedly improved.

x \fallingdotseq 0.15

The authors present high-quality p-type SiGe double barrier resonant tunneling diodes obtained from bulk SiGe substrates grown by the multicomponent zone-melting method and by the layer deposition with molecular beam epitaxy. Devices exhibit a high peak-to-valley current ratio up to 8.8 at 4.2K and a negative differential resistance up to 340K. The result demonstrates that bulk SiGe substrates have a clear potential impact for fabricating high-performance SiGe heterostructure devices based on quantum transport.

) Bulk Crystal with Uniform Composition Utilizing in situ Monitoring of the Crystal-solution Interface

A detailed study of molecular beam epitaxy of GaAs on homemade SiGe substrates has been performed. It was found that the initial migration-enhanced epitaxy process with As prelayer is crucial to obtain high-quality GaAs. By (004) x-ray diffraction, the lattice mismatch between GaAs and SiGe was demonstrated to be reduced compared with the conventional GaAs/Ge heterostructure. Furthermore, narrower halfwidth of the rocking curve and stronger photoluminescence intensity were found for GaAs on SiGe. These results show that SiGe is a promising material as an alternative substrate to Ge to realize exact lattice matching to GaAs for solar cell applications.

SiGe double barrier resonant tunneling diodes on bulk SiGe substrates with high peak-to-valley current ratio

Growth of binary and ternary single crystals which have complete miscibility in the phase diagrams, have been studied by several newly developed methods such as the liquid encapsulated Czochralski, Bridgman, and multi-component zone melting methods for InGaAs bulk crystals, and the multi-component zone melting methods and Bridgman methods for Ge-rich and Si-rich SiGe bulk crystals. Crystals grown by these methods are compared with each other, to find the proper growth conditions to obtain single crystals with uniform composition. Techniques for the precise control of the temperature at the growing interface and for the continuous supply of the depleted solute elements to the growth melt were developed. InGaAs bulk crystals with uniform composition were obtained by the multicomponent zone melting method. Si-rich and Ge-rich SiGe bulk crystals with uniform composition were obtained in the Ge compositional range from 10 to 78%. The advanced technologies to obtain the InGaAs and SiGe bulk crystals with much higher-quality are discussed in this paper.

Molecular beam epitaxy of GaAs on nearly lattice-matched SiGe substrates grown by the multicomponent zone-melting method

Abstract SiGe bulk crystal was grown by the multicomponent zone-melting method equipped with an in situ monitoring system of the position and the temperature at the crystal-solution interface. By utilizing the in situ monitoring system, an attempt was made to control the interface position at a fixed position during growth by balancing the growth rate and the pulling rate of the crystal. This led to realization of SiGe bulk crystal with Ge composition of 0.86±0.004 over 22 mm in length. However, as growth proceeds, development of small angle boundaries was evidenced by X-ray characterizations. This polycrystallization was found to be accompanied with appearance of deep-level emission in photoluminescence spectra. A preliminary result to grow SiGe with intermediate composition, which is important for Si-based heterostructures, was also performed.

Growth of InGaAs and SiGe homogeneous bulk crystals which have complete miscibility in the phase diagrams

We attempted to utilize a GaAs single crystal with preferential orientation as a seed to obtain an InGaAs single bulk crystal. The preferential orientation of the InGaAs bulk crystal was determined as [110] in a preliminary experiment to utilize multiple seed crystals with random orientations. By subsequent zone growth of InGaAs on GaAs(110), an InxGa1-xAs (x>0.18) single bulk crystal with a diameter of 15 mm and a length of 13 mm was successfully obtained on the seed without a compositionally graded InGaAs layer. The large lattice mismatch between GaAs and InGaAs was likely to be accommodated by an array of thin columnar grains at the interface.