Inductively coupled plasma etching of InGaP, AllnP, and AlGaP in Cl2 and BCl3 chemistries

Dry etching of InGaP, AlInP, and AlGaP in inductively coupled plasmas (ICP) is reported as a function of plasma chemistry (BCl₃ or Cl₂, with additives of Ar, N₂, or H₂), source power, radio frequency chuck power, and pressure. Smooth anisotropic pattern transfer at peak etch rates of 1000–2000Å·min^?1 is obtained at low DC self-biases (?100V dc) and pressures (2 mTorr). The etch mechanism is characterized by a trade-off between supplying sufficient active chloride species to the surface to produce a strong chemical enhancement of the etch rate, and the efficient removal of the chlorinated etch products before a thick selvedge layer is formed. Cl₂ produces smooth surfaces over a wider range of conditions than does BCl₃.     

Effects of high temperature annealing on the device characteristics of Ga0.52In0.48P/GaAs and Al0.52In0.48P/GaAs heterojunction bipolar transistors

GaInP/GaAs and AlInP/GaAs heterojunction bipolar transistor (HBT) structures were grown by low pressure metalorganic vapor phase epitaxy and annealed at various temperatures up to 675°C for 15 min. Subsequent comparisons with HBTs fabricated on both annealed and unannealed control samples showed no effects for annealing up to and including 575°C, but significant changes in the electrical characteristics were observed at an annealing temperature of 675°C. For the GaInP/GaAs devices, the base current increased by a significant amount, reducing the gain and increasing the base current ideality factor from 1.07 to 1.9. Photoluminescence and electrical measurements on the structures indicated that both the emitter and base were affected by an increase in the recombination times in those regions. These effects were attributed to an out-diffusion of hydrogen from the base during annealing. The emitter of the AlInP/GaAs HBT was affected less by the hydrogen diffusion because of the larger bandgap. These observations have important implications for device performance dependence on the details of the temperature/time profile subsequent to the base growth.     

Determination of the Band Offset of GalnP- GaAs and AllnP- GaAs Quantum Wells by Optical Spectroscopy

We report the determination of band offset ratios, using photoluminescence excitation measurements, for GaInP/GaAs and AlInP/GaAs quantum wells grown by gas-source molecular beam epitaxy. To reduce the uncertainty related to the intermixing layer at heterointerfaces, the residual group-V source evacuation time was optimized for abrupt GalnP/GaAs (AlInP/GaAs) interfaces. Based upon thickness and composition values determined by double-crystal x-ray diffraction simulation and cross-sectional transmission electron microscopy, the transition energies of GalnP/GaAs and AlInP/GaAs quantum wells were calculated using a three-band Kane model with varying band-offset ratios. The best fit of measured data to calculated transition energies suggests that the valence-band offset ratio (γ band discontinuity) was 0.63 ± 0.05 for GalnP/GaAs and 0.54 ± 0.05 for AlInP/GaAs heterostructures. This result showed good agreement with photoluminescence data, indicating that the value is independent of temperature.     

Growth and properties of digitally-alloyed AlGaInP by solid source molecular beam epitaxy

Digital alloying using molecular beam epitaxy (MBE) was investigated to produce AlGaInP quaternary alloys for bandgap engineering useful in 600-nm band optoelectronic device applications. Alternating Ga_0.51In_0.49P/Al_0.51In_0.49P periodic layers ranging from 4.4 monolayers (ML) to 22.4 ML were used to generate 4,000-Å-thick (Al_0.5Ga_0.5)_0.51In_0.49P quaternary materials to understand material properties as a function of constituent superlattice layer thickness. High-resolution x-ray diffraction (XRD) analysis exhibited fine satellite peaks for all the samples confirming that digitally-alloyed (Al_0.5Ga_0.5)_0.51In_0.49P preserved high structural quality consistent with cross-sectional transmission electron microscopy (X-TEM) images. Low-temperature photoluminescence (PL) measurements showing a wide span of luminescence energies ～ 170 meV can be obtained from a set of identical composition digitally-alloyed (Al_0.5Ga_0.5)_0.51In_0.49P with different superlattice periods, indicating the bandgap tunability of this approach and its viability for III-P optoelectronic devices grown by MBE.     

MOVPE growth of AlxIn1−xP using tertiarybutylphosphine in pure N2 ambient

We have investigated metalorganic vapor phase epitaxy (MOVPE) growth of Al_xIn_1−xP alloy using tertiarybutylphosphine (TBP) as the phosphorus source in pure N₂ ambient. The effect of the substrate temperature on the aluminum composition of Al_xIn_1−xP epilayers during the MOVPE growth has been studied. When the source flow rates were kept unchanged, the aluminum composition of the Al_xIn_1−xP epilayer increased monotonically when the substrate temperature, T_g, was raised from 580 °C to 660 °C during the growth. It became saturated when T_g reached 660 °C and above. The crystalline quality of the grown Al_xIn_1−xP epilayers has been investigated by X-ray diffraction and photoluminescence measurements. A linear relationship between the aluminum composition of the Al_xIn_1−xP epilayer and TMAl/(TMAl + TMIn) source flow ratio has been obtained when grown at the optimized growth temperature of T_g = 630 °C. It has also been observed that the aluminum incorporation coefficient of Al_xIn_1−xP epilayers decreased when the V/III source flow ratio was increased during the MOVPE growth.     

Oxygen-related deep levels in Al0.5In0.5P grown by MOVPE

Oxygen related defects in Al-containing materials have been determined to degrade luminescence efficiency and reduce carrier lifetime and affect the performance of light emitting diodes and laser diodes utilizing these materials. We have used the;metal-organic source diethylaluminum ethoxide (DEAlO) to intentionally incorporate oxygen-related defects during growth of Al_0.5In_0.5P by metal-organic vapor phase epitaxy (MOVPE). The incorporated oxygen forms several energy levels in the bandgap with energies of 0.62 eV to 0.89 eV below the conduction band detected using deep level transient spectroscopy. Secondary ion mass spectroscopy measurements of the total oxygen concentration in the layers shows a direct correlation to the measured trap concentrations. Several other energy levels are detected that are not correlated with the oxygen content of the film. The possible origin of these additional levels is discussed.     

Oxygen incorporation in AllnP, and its effect on P-type doping with magnesium

Oxygen incorporation in Al_yIn_1−yP (y ∼ 0.5) grown by metalorganic chemical vapor deposition (MOCVD) has been studied as a function of PH₃ flow, growth temperature, and alloy composition. Both O₂ and diethylaluminum ethoxide (DEAlO) were employed as sources of oxygen. The incorporation of oxygen was found to be a superlinear function of O₂ or DEAlO flow. When multiple sources of oxygen are present, a surface interaction leads to enhanced oxygen incorporation. Oxygen incorporation cannot be adequately described by a simple dependence on growth temperature or V/III ratio due to strong interactions between these variables. In Mg-doped AlInP co-doped with oxygen, the incorporation of both Mg and O is strongly affected by an interaction between the two species, and roughly 10% of the oxygen atoms act as compensating donors.     

Dry etching of InGaAlP alloys in Cl2/Ar high ion density plasmas

Etch rates above 1 μm min⁻¹ are achieved for InGaP and AlInP under electron cyclotron resonance conditions in low pressure (1.5 mTorr) Cl₂/Ar discharges. Much lower rates were obtained for AlGaP due to the greater difficulty of the bond breaking that must precede formation and desorption of the etch products. The etched surface morphology and stoichiometry are strong functions of the plasma composition (i.e., the ion/neutral flux ratio). Under optimal conditions, there are no detectable chlorine related residues, in sharp contrast to reactive ion etching with this plasma chemistry.     

GaInP and AlInP grown by elemental source molecular beam epitaxy

We report on the use of a new, valved, solid phosphorus cracker source for the growth of phosphides by molecular beam epitaxy. The source avoids the relatively high expense and high level of toxicity associated with the use of phosphine gas and eliminates the problems commonly encountered in using conventional solid phosphorus sources. The source has been used to grow GaInP and AlInP lattice-matched to GaAs substrates. The quality of the materials reported here is comparable to the best materials grown by other techniques. Photoluminescence and Raman scattering measurements indicate that the resulting material has a high degree of disorder on the group III sublattice. The new source is shown to be a reliable and attractive alternative for the growth of these phosphide materials.