However, following the work of Alferov and co-workers, the solid-state group at Varian Associates proposed a quaternary alloy of 50% (Ga-In) and 50% (As-P) that could in principle be grown lattice matched on an InP substrate (Antypas et al. 1973). By doing so this group enunciated the principles by which a general semiconductor alloy could be grown on a particular substrate (presumably one that is inex-pensive to obtain) while maintaining the lattice par-ameter of the alloy layer equal to that of the substrate.This revolutionary idea remained unexploited by all but Varian Associates; they used it to produce GaxIn1−xAsyP1−y photocathode photomultiplier tubes for IR detection out to 1.1lm. These detectors, costing over US$10,000 in 1970 were unique. Unfortunately there were few customers because IR sources emitting at 1.1lm (beside the light bulb) were unknown at the time.
The push to develop this new materials system came from the discovery that glass optical ®bers for tele- communications required optical sources and de-tectors at 1.3lm and 1.5lm, and not at 0.85lm where GaAs lasers function. Even strained ternary alloys of GaAs such as Ga-As-Sb and Ga-In-As with a bandgap corresponding to this wavelength could not be grown in single-crystal form on GaAs. In the mid-1970s the first solid-state devices based onGaxIn1−xAsyP1−y were developed (Pearsall et al. 1976,Hsieh 1976). Materials in this alloy range span nearly a factor of two in bandgap energy, from 0.75eV(Ga0.47In0.53As, y=1) to 1.35eV (InP, y=0). The diagram of the fundamental bandgap vs. lattice parameter in Fig. 1(a) shows this range along the vertical line B. There is an additional line A for the epitaxial growth of Ga1−xInxAs1−yPy on GaAs substrates while conserving the lattice parameter of GaAs. Note carefully that in this case the roles of both gallium and indium and of arsenic and phosphorus are exchanged. These alloys span the bandgap range from1.43eV (GaAs, y=0) to 1.9eV (Ga0.51In0.49P, y=1).However, this alloy system spans nearly the same bandgap range as that of the AlGaAs system, and is not frequently exploited in devices. Continuing up-ward along line A, one encounters a new quaternaryalloy (AlyGa1−y)xIn1−xP. In combination withGa1−xInxPy(y=1, x=0.49), this system is extensively used for the fabrication of visible laser diodes for scanners and optical disk players. The solid phase diagram for this quaternary alloy is shown in Fig. 1(b).The substrate materials that can be used with these GaInAsP systems are GaAs and InP. After silicon, of course, these materials are the most often used for semiconductor substrates and are readily available (Adachi 1992, Agrawal and Dutta 1986, Bhattacharya 1993, Madelung et al. 1982, Pearsall 1982, 2000).
In this article, some basic materials parameters of GaxIn1−xAsyP1−yfor compositions that can be readily grown lattice matched on InP are compiled. Where possible, theory has been used to estimate the proper-ties of the Ga1−xInxAs1−yPy alloy system for com- positions that can be grown lattice-matched on GaAs.In addition we note other excellent and comprehensive reviews covering materials properties, epitaxial growth, and device applications of this technologically important system of semiconductor alloys.
► The thermal conductivity of InAs on InP (1 1 3)B quantum dots stacks is measured.
► The growth of a close stack of 100 layers of InAs using AlAs strain compensating layers is presented.
► New data on the thermal conductivity of InP n-doped susbtrate are given.
Source: Materials Science and Engineering: B
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