Progress in Crystal Growth and Characterization最新文献

Atmospheric pressure organometallic vapor phase epitaxy is used for the growth of GaInP-AlGaInP lattice matched to GaAs substrate. The investigation of the GaInP/GaAs heterostructure has been carried out and mobility as high as 75 000 cm² V^-1s^-1 for a sheet carrier concentration of 7.5 10¹¹ cm^-2 has been measured by Shubnikov-de Haas at 4 K. Red and yellow LED's have been obtained with emission wavelength of 670 nm and 576 nm respectively. Oxide stripe laser emitting at 660 nm in pulsed mode have been performed and present a threshold current density of 5 kA cm^-2. Three ridge waveguide laser diode arrays with maximum output power of 108 mW have also been achieved.

A comprehensive evaluation of the T-shaped reactor, in view of its use as a production tool for 1300 nm optoelectronic devices, was carried out. The material obtained was of excellent quality and exhibited a very high degree of uniformity and good reproducibility, despite the difficulties associated with the control of two composition ratios, particularly with the As/P one. The extension to other compositions is obvious. Ternary and quasi-ternary materials ( InGaAs, InGaAlAs ) can be handled with even greater ease, not to speak about binaries and quasi-binaries ( GaAs, GaAlAs ). The system lends itself naturally to extension toward larger wafer sizes. A multi-wafer system based on the same principles can also be implemented ; very recently, such a system was proposed by Frijlink [16].

The existence of a modulated structure is signified in reciprocal space by the existence of weak extra features in addition to the strong Bragg reflections of the unmodulated parent structures. These weak extra features may be sharp incommensurate satellite reflections and/or a diffuse intensity distribution. The extraction of information as regards the character of such modulated structures from a study of their diffraction patterns is reviewed. In Section 2, the structural parameters defining the deviation of modulated structures from their corresponding parent phases is discussed. In Section 3, the observation and interpretation of satellite extinction conditions is discussed. In Section 4 and 5, the qualitative features often present in the diffraction patterns of modulated structures are related to structure factor expressions.

Recent developments in the bulk Bridgman growth method for Cd_xHg_1−xTe are reviewed. Both melt mixing and heat flow control techniques have been applied in attempts to produce more uniform material in terms of composition. In the U.K. work has concentrated on application of the Accelerated Crucible Rotation Technique (ACRT) to achieve the required uniformity improvements. Elsewhere, various means to control isotherm shape have been used with the same aim. The ultimate use of the material is in infra-red detectors and Bridgman grown Cd_xHg_1−xTe has produced these successfully for both photoconductive and photovoltaic applications.

Extrinsic doping by elements which are stable to subsequent processing will become increasingly important in future infra-red device structures based on Cd_xHg_1−xTe. This paper reviews the incorporation and activation of dopants in the most widely used bulk and epitaxial growth methods. Stoichiometry at the growth temperature is shown to be the critical factor affecting dopant activation. Various factors, including stoichiometry, can affect the as-grown electrical properties and the importance of determining the type of conduction in the as-grown state, if successful extrinsic doping is to be accomplished, is stressed. Data on dopant segregation behaviour, in growth from liquids, acceptor ionization energies and carrier lifetimes are also presented and their importance is discussed.

The evolution of the MOVPE growth technology has led to highly pure materials and to complex multi-layer structures. In turn this has led to new challenges for the characterisation of materials, and experimental methods are also evolving to meet this challenge. In this review we attempt to focus attention on techniques which probe some of the key materials parameters for advanced structures: Ultra high purity layers and atomically sharp systems.