Composition In0 Research Articles

Properties and use of ln0.5(AlxGa1-x)0.5P and AlxGa1-x as native oxides in heterostructure lasers

Data are presented demonstrating the formation of native oxides from high Al composition In0.5(AlxGa1-x)0.5P (x≳ 0.9) by simple annealing in a “wet” ambient. The oxidation occurs by reaction of the high Al composition crystal with H2O vapor (in a N2 carrier gas) at elevated temperatures (≥500° C) and results in stable transparent oxides. Secondary ion mass spectrometry (SIMS) as well as scanning and transmission electron microscopy (SEM and TEM) are employed to evaluate the oxide properties, composition, and oxide-semiconductor interface. The properties of native oxides of the In0.5(AlxGa1-x)0.5P system are compared to those of the AlxGa1-xAs system. Possible reaction mechanisms and oxidation kinetics are considered. The In0.5(AlxGa1-x)0.5P native oxide is shown to be of sufficient quality to be employed in the fabrication of stripe-geometry In0.5(AlxGa1-x)0.5P visible-spectrum laser diodes.

New high T c superconductor: (In,Pb,Cu)Sr2(Ca,Y)Cu2O7−δ

Bulk superconductivity was observed in the new system (InxPb0.75−xCu0.25)Sr2(Ca0.5Y0.5)Cu2 O7−δ. An increase in indium doping, 0≤x≤0.2, into the Pb sites results in an increase in the superconducting transition temperature Tc from 45 K for x=0 to 60 K for x=0.2. For nominal compositions x≳0.2, a decrease in Tc was observed, and an increase in the concentration of an impurity phase. From the results of the x-ray diffraction and energy- dispersive spectrometry, we identify the phase responsible for the superconductivity to be [In0.06(1)Pb0.69(1)Cu0.25]Sr1.99(7)[Ca0.47(1)Y 0.53(2)]Cu2O7−δ; this phase resulted from the synthesis of a sample of nominal composition (In0.2Pb0.55Cu0.25)Sr2(Ca0.5Y0.5)Cu2 O7−δ.

Dry etching characteristics of In1-x-y Ga x Al y as alloys in CCl2F2:Ar and CH4:H2:Ar discharges

The etching characteristics of InGaAlAs alloys lattice-matched to InP were investigated using low pressure (1 mTorr) electron cyclotron resonance CH4:H2:Ar or CCl2F2:Ar discharges with additional radiofrequency biasing of the samples. Using CCl2F2:Ar discharges with ≥250V negative bias it is possible to obtain equi-rate etching of the material for all compositions between In0.53Ga0.47As and In0.52Al0.48As. At lower bias values, formation of A1F3 on the surface leads to an inhibition of the etch rates. By making use of the differential etch rates of InGaAlAs layers of different compositions in CH4:H2:Ar mixtures, it is possible to choose dc bias values that allow one to stop the etching at a pre-selected depth in a multi-layer structure. For example, for -150 V bias, one can etch through In0.53Ga0.47As, In0.53Ga0.40Al0.07As and Ino.53Ga0.30Al0.17As layers, and stop at an underlying layer with composition In0.53Ga0.20Al0.27As.

Native-oxide stripe-geometry In0.5(AlxGa1−x)0.5P-In0.5Ga0.5P heterostructure laser diodes

Data are presented demonstrating the formation of stable, device-quality native oxides from high Al composition In0.5(AlxGa1−x)0.5P (x ∼0.9) via reaction with H2O vapor (in N2 carrier gas) at elevated temperatures (≥500 °C). The oxide exhibits excellent current-blocking characteristics and is employed to fabricate continuous room-temperature stripe-geometry In0.5(AlxGa1−x)0.5P-In0.5Ga0.5P double-heterostructure laser diodes.

Stable and shallow PdIn ohmic contacts to n-GaAs

A thermally stable, low-resistance PdIn ohmic contact to n-GaAs has been developed based on the solid phase regrowth mechanism [T. Sands, E. D. Marshall, and L. C. Wang, J. Mater. Res. 3, 914 (1988)]. Rapid thermal annealing of a Pd-In/Pd metallization induces a two-stage reaction resulting in the formation of a uniform single-phase film of PdIn, an intermetallic with a melting point greater than 1200 °C. A thin (∼5 nm) layer of average composition In0.4Ga0.6 As uniformly covers the interface between the PdIn layer and the GaAs substrate. Specific contact resistivities and contact resistances of ∼1×10−6 Ω cm2 and 0.14 Ω mm, respectively, were obtained for samples annealed at temperatures in the 600–650 °C range. The addition of a thin layer of Ge (2 nm) to the first Pd layer extends the optimum annealing temperature window down to 500 °C. Specific contact resistivities remained in the low 10−6 Ω cm2 range after subsequent annealing at 400 °C for over two days.

High-resolution x-ray diffraction and transmission electron microscopy studies of InGaAs/InP superlattices grown by gas-source molecular beam epitaxy

A three-crystal geometry has been used for high-resolution x-ray diffraction (XRD) along with lattice imaging transmission electron microscopy (TEM) to study two high-quality InGaAs/InP multiquantum well structures grown on (100) InP. These superlattices were prepared by gas-source molecular beam epitaxy using a computer controlled system and were found to have excellent optical properties. Cross-section TEM and the presence of sharp satellite reflections in the XRD profiles demonstrate very smooth interfaces with well-defined modulated structures which could be derived from a kinematic XRD step model. For one of these superlattices, excellent agreement between the step model and the measurements is obtained when the model assumes that each period consists only of the well and the barrier with ideally sharp interfaces. For the other superlattice an additional approximately 9-Å-thick layer of approximate composition In0.47Ga0.53As0.985P0.015 had to be assumed on one side of each quantum well. This additional layer is attributed to substitution of ambient P for 1.5 at. % of the As during growth interruption and is easily eliminated. The comparison of these two structures demonstrates the extreme sensitivity of the high-resolution XRD method in conjunction with the step model to study very small modifications in superlattice characteristics.

Quaternary Alloy Infrared Heterojunction Detectors

Single heterojunction photodiodes suitable for the 1.0 to 1.3 pm spectral region of interest for fiber optics communication have been prepared from lattice-matched p-type epilayers of the quaternary III-V alloy semiconductor InGaAsP on n-type InP substrates. The characteristics of these heterojunctions are demonstrated by mesa photodiodes made from Zn-doped epilayers of composition In0.84Ga0.16Aso.34P0.66 on Sn-doped InP. Their room temperature spectral response extends from the ~0.96 um self-filtering cutoff of the InP substrate to (~1.13 um determined by the bandgap of this particular quaternary composition. Responsivities of 0.46 A/W and external quantum efficiencies of 0.54 are measured at 1.05 um.

Band Structure of InGaP from Pressure Experiments

Positive identification of the Γ and X conduction-band minima in InGaP has been made by performing hydrostatic-pressure experiments on forward-biased p-n junction diodes. The Γ and X valleys are coincident in energy at a composition of In0.37Ga0.63P, and the corresponding bandgap is (2.17±0.02) eV at 300°K. The indirect bandgap EX in InP is inferred from the measurements to be 2.0 eV at 300°K. In addition, the pressure coefficients of the direct and indirect bandgaps, ∂EΓ/∂P and ∂EX/∂P, respectively, have been measured at various In(1−x)GaxP compositions. For InP, ∂EΓ/∂P is 8.7×10−3 eV/kbar and this coefficient increases to 13×10−3 eV/kbar for compositions close to In0.5Ga0.5P. On the other hand, ∂EX/∂P = −1.25×10−3 eV/kbar for GaP and shows little change for compositions in the range 0.4<x<1. The deformation potential is 5.7 eV for the Γ valley in InP, and increases to about 9 eV for direct bandgap ternary compositions.