InGaAsP Epilayers Research Articles

Properties of undoped and manganese-doped InGaAsP grown by liquid phase electroepitaxy

Undoped and manganese-doped InGaAsP epilayers lattice matched to InP substrate have been grown by the liquid phase electroepitaxy technique. The dependence of growth velocity on current density for both undoped and doped layers has been studied. Layers of good surface morphology with hole concentrations in the range from 8 × 10 16 to 4 × 10 18 cm -3 have been achieved. The activation energy of the manganese acceptor level was estimated to vary from 57 to 32 meV with increasing hole concentration. The temperature dependence of carier mobility data was analyzed in terms of different scattering mechanisms and the values of acceptor and donor densities determined were compared with those obtained from the temperature variation of Hall concentration data. Dependences of photoluminescence peak energy and intensity on the temperatyre and incident excitation levels have been investigated.

Optically controlled transmission of InGaAsP epilayers

We investigate the transmission of InGaAsP epilayers lattice matched to InP substrates under optical excitation at normal incidence to the surface. Near the gap wavelength (lambda = 1.3 microm) we observe a transmission change of 20% for a 0.5-mW pump beam at a wavelength lambda(2) = 790 nm. Switching dynamics are shown to be limited by carrier lifetimes of tau approximately 2 nsec. A simple analysis based on parabolic bands and direct electronic transitions provides a good description of the experiments.

Study of supercooling behaviour of InGaAsP solutions for growth of high quality InGaAsP/InGaAs(P) layers on (100) InP

The growth conditions for producing high quality InGaAsP(λ=1.3 μm)/In 0.53Ga 0.47As interfaces on (100) oriented InP by liquid phase epitaxy were investigated in detail. Results on the variation of InGaAsP layer thickness, lattice mismatch and photoluminescene wavelength with growth temperature reveal that homogeneous nucleation of the quaternary growth melt occurs at a critical supercooling δ T c. Four growth regimes, δ T > δ T c and δ T < δ T c in both the presence and absence of apparatus vibration were evaluated. High quality InGaAsP/InGaAs interfaces can be grown at melt cooling rates as low as 0°C/min for δ T < δ T c in the absence of vibration, but vibration will slightly degrade interface quality. For δ T > δ T c, melt cooling rates of ≈0.6°C/min i the absence of apparatus vibration will yield good interfaces; but melt cooling rates ≤ 0.1°C/min and/or apparatus vibration will result in very poor quality interfaces. Attack of InGaAsP (λ=1.55 μm) epilayers by quaternary melts with δ T > δ T c and low melt cooling rates was also observed.

Zn contamination in InGaAsP/InP DH structure grown by LPE

The Zn auto-doping phenomenon of DH structures grown by LPE was evaluated, using photoluminescence (PL) and SIMS analyses. From these analyses, it was found that Zn contamination of an undoped epitaxial film is rather large when a highly Zn-doped melt is adjacent to an undoped melt, and this amount is 5% of the total Zn doping level. But, if the melts are separated, the contamination can be much decreased to only 0.5% and as a result the undoped InGaAsP epi-layer contains much less Zn introduced from the heavily Zn doped InP layer.

Characterization of epitaxial In0.75Ga0.25As0.56P0.44 layers on InP grown by liquid phase epitaxy

The step cooling technique for liquid phase epitaxy was used to grow In0.75Ga0.25As0.56P0.44 thin films on InP substrates. The optimum growth temperature is 635°C with a supercooling temperature (δT) of 10°C. Under these conditions, the lattice mismatches between epilayers and substrates were less than 0.03% as determined by X-ray diffraction measurements. The solid composition was studied. From optical transmission measurement, the corresponding wavelength of the quaternary layer was 1.28 μ m. The quality of the In0.75Ga0.25As0.56P0.44 epitaxial layers was studied by using the diffraction patterns from transmission electron microscopy. The measured room temperature mobility and carrier concentration of undoped InGaAsP epilayers were 3200 cm2/Vh.s and 1.76 x 1016 cm−3, respectively.

Formation of optically induced catastrophic degradation lines in InGaAsP epilayers

The formation of optically induced catastrophic degradation lines (CDL’s) in (001) InGaAsP epitaxial layers has been investigated by transmission electron microscopy. It appears that CDL’s evolve as a result of the temperature-gradient-induced migration of liquid droplets. These droplets could form in pre-existing regions where nonradiative recombination during optical pumping is very high. Further, the propagation of droplets involves dissolution followed by rapid deposition. Consequently, the resulting microstructures are highly defective and consist of decorated dislocations, loops, and precipitates. These features could act as nonradiative recombination centers and thus degrade the material. CDL’s propagate only along the 〈110〉 direction which is common to the {111}In,Ga and (001) planes. In addition, the Burgers vector of dislocations constituting a CDL is parallel to the direction of its propagation. Arguments have been developed to rationalize these observations.

Liquid phase epitaxy of unstable alloys: Substrate-induced stabilization and connected effects

It is now well admitted that most quaternary III–V compounds show unstable regions in the temperature range commonly used in epitaxy. For instance, according to these authors, the InGaAsP alloy, lattice matched to InP and with emitting wavelength 1.3 μm should be unstable at temperatures below 700 °C. Liquid phase epitaxy, however, is commonly performed down to 600 °C. As this growth technique occurs close to thermodynamical equilibrium, such growth should not take place. It was clearly demonstrated that the substrate stabilizing effect is responsible for this paradoxical behavior. Another LPE substrate effect pointed out by Stringfellow is known as the ‘‘pulling effect.’’ Results will be presented showing the connection between these effects in the system InGaAsP/InP and particularly InGaAs/InP. ‘‘Stabilized’’ GaAsSb was also successfully epitaxially grown on InP, in the immiscibility region, from the liquid phase. Microscopic compositional periodical modulations are observed in standard InGaAsP epilayers, if growths are performed below a critical temperature. This phenomena, also related to solid instability, can be interpreted in terms of liquid–solid interfacial spinodal decomposition.

The status of current understanding of InP and InGaAsP materials

A brief review of the status of current understanding of as-grown InP crystals and InGaAsP materials, problems associated with thermal-induced decomposition of these materials and mechanisms of degradation of InGaAsP epilayers is presented.

The Interrelationship Between Structure and Properties in InP and InGaAsP Materials

ABSTRACTThree examples pertaining to the influence of heavy doping on the microscopic perfection of as-grown InP crystals, thermal decomposition of InP crystals and epi-layers and optically induced degradation of InGaAsP epi-layers have been chosen to delineate some of the correlations observed between microstructure and properties in these materials. It is shown that the macroscopic perfection can be significantly improved by highly doping with Zn, S, and Se. However, in the case of Zn, not all of the dopant atoms are in solid solution and some of them have clustered to form precipitates, whereas these features are not seen in highly S- and Se-doped crystals.Thermal decomposition of epi-layers introduces areas which appear dark in a photoluminescence scan. It is argued that these regions evolve due to the out diffusion of P. In addition, when InP epi-layers are grown on thermally-decomposed substrates, dislocation density in the epi-layers is higher than that in the substrate. Arguments have been developed to rationalize these observations.Non-luminescent regions develop in InGaAsP epilayers by optical pumping. These areas are associated with dislocation clusters which appear to evolve by glide of the existing dislocations.