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.     

Electrical passivation in hydrogen plasma exposed GaN

Lightly p-doped (3×10¹⁷ cm^-3) GaN grown on GaAs substrates by metal organic molecular beam epitaxy (MOMBE) shows deactivation of the residual acceptors on exposure to a microwave (2.45 GHz) hydrogen plasma at 250°C. Subsequent annealing to 350°C produces further dopant passivation, while higher temperatures (450°C) restore the initial conductivity. These results suggest that hydrogen carrier gases should be avoided during vapour phase growth of III-V nitrides     

Effect of ion energy on hydrogen diffusion in n- and p-GaAs

The ion energy during electron cyclotron resonance (ECR) plasma hydrogenation is found to have a strong effect on both the effective diffusivity and solubility of hydrogen in n⁺ and p⁺ GaAs. For fixed plasma exposure conditions (30 min, 250°C) the diffusion depths for -150 V acceleration voltage are ~50 and ~100% larger, respectively, in p⁺- and n⁺-GaAs compared to 0 V acceleration voltage. The smaller incorporation depths at lower ion energy coincide with much larger peak hydrogen concentrations and higher apparent thermal stability of passivated dopants     

High-power 980-nm AlGaAs/InGaAs strained quantum-well laser grown by OMVPE

High-power lattice-strained AlGaAs/InGaAs graded index separate-confinement heterostructure (GRINSCH) quantum-well lasers emitting at a 980-nm wavelength have been grown by organometallic vapor phase epitaxy (OMVPE) and fabricated with a self-aligned ridge-waveguide structure. Using a 3- mu m-wide and 750- mu m-long AR-HR coated laser, 30 mV of optical power was coupled into optical fibers with 28.6% efficiency. A dominating single-lobe far-field radiation pattern was obtained from a wedge-shaped ridge-waveguide laser for output power as high as 240 mW with a maximum output power of 310 mW.<>     

Magnetism in SiC implanted with high doses of Fe and Mn

High concentrations (0.1–5 at.%) of Mn or Fe were introduced into the near-surface region (≤2000 Å) of 6H-SiC substrates by direct implantation at ～300°C. After annealing at temperatures up to 1000°C, the structural properties were examined by transmission electron microscopy (TEM) and selected-area diffraction pattern (SADP) analysis. The magnetic properties were examined by SQUID magnetometry. While the Mn-implanted samples were paramagnetic over the entire dose range investigated, the Fe-implanted material displayed a ferromagnetic contribution present at <175 K for the highest dose conditions. No secondary phases were detected, at least not to the sensitivity of TEM or SADP.     

Selective and nonselective wet etching of Zn0.9Mg0.1O/ZnO

Wet etch rates at 25°C for Zn_0.9Mg_0.1O grown on sapphire substrates by pulsed laser deposition (PLD) were in the range 300–1100 nm · min⁻¹ with HCl/H₂O (5×10⁻³−2×10⁻² M) and 120–300 nm · min⁻¹ with H₃PO₄/H₂O (5×10⁻³−2×10⁻² M). Both of these dilute mixtures exhibited diffusion-limited etching, with thermal activation energies of 2–3 kCal · mol⁻¹. By sharp contrast, the etch rates for ZnO also grown on sapphire by PLD were much slower in similar solutions, with rates of 1.2–50 nm · min⁻¹ in HCl/H₂O (0.01–1.2 M) and 12–54 nm · min⁻¹ in H₃PO₄/H₂O (0.02–0.15 M). The etching was reaction limited over the temperature range 25–75°C, with activation energies close to 6 kCal · mol⁻¹. The resulting selectivity of Zn_0.9Mg_0.1O over ZnO can be a high as ∼400 with HCl and ∼30 with H₃PO₄.     

Fabrication and characteristics of high-speed implant-confined index-guided lateral-current 850-nm vertical cavity surface-emitting lasers

Process technology of high-speed implant-apertured index-guide lateral-current-injection top dielectric-mirror quantum-well 850-nm vertical cavity surface-emitting lasers (VCSELs) has been developed. Oxygen and helium implantation for aperture definition and extrinsic capacitance reduction, dielectric mirror formation, p- and n-ohmic contact formation, VCSEL resistance, and thermal analysis were investigated. Employing this technology, GaAs/AlGaAs-based 850-nm VCSELs with small signal modulation bandwidths up to 11.5 Gb/s and an eye diagram generated at 12 Gb/s by a pseudorandom bit sequence of 2/sup 31/-1 were achieved. The bit-error rates were below 10/sup -13/. The threshold current is as low as 0.8 mA for 7-/spl mu/m-diameter current apertures and typical slope efficiencies of 0.45-0.5 mA/mW were obtained.     

Effects of Sc2O3 and MgO passivation layerson the output power of AlGaN/GaN HEMTs

The low temperature (100°C) deposition of Sc₂O₃ or MgO layers is found to significantly increase the output power of AlGaN/GaN HEMTs. At 4 GHz, there was a better than 3 dB increase in output power of 0.5×100 μm² HEMTs for both types of oxide passivation layers. Both Sc₂ O₃ and MgO produced larger output power increases at 4 GHz than conventional plasma-enhanced chemical vapor deposited (PECVD) SiN_x passivation which typically showed ⩽2 dB increase on the same types of devices. The HEMT gain also in general remained linear over a wider input power range with the Sc₂O₃ or MgO passivation. These films appear promising for reducing the effects of surface states on the DC and RF performance of AlGaN/GaN HEMTs     

Science of dry etching of III-V materials

A review is given of dry etching of III-V semiconductors. Gas chemistries based on chlorine have traditionally been used for plasma etching of these materials due to the volatilities of both group III and group V chlorides. Recent work on the use of iodine- or bromine-based discharges has shown promising results, although the corrosiveness of the feedstock gases is of concern. For indium-containing III-V semiconductors, CH₄/H₂ plasmas have produced smooth anisotropic etching at relatively low rates. In applications requiring etch rates near 1 m min^–1, Cl₂/CH₄/H₂ electron cyclotron resonance discharges have proved effective. Examples are given of the structural and chemical changes induced in the semiconductor as a result of dry etching, due to the combined effects of energetic ion bombardment and preferential removal of one of the lattice constituents. Applications for dry etching in modern microelectronic fabrication range from shallow (30 nm) mesa formation to creation of through-wafer via holes typically 100 m deep.     

Design of edge termination for GaN power Schottky diodes

The GaN Schottky diodes capable of operating in the 300–700-V range with low turn-on voltage (0.7 V) and forward conduction currents of at least 10 A at 1.4 V (with corresponding forward current density of 500 A/cm²) are attractive for applications ranging from power distribution in electric/hybrid electric vehicles to power management in spacecraft and geothermal, deep-well drilling telemetry. A key requirement is the need for edge-termination design to prevent premature breakdown because of field crowding at the edge of the depletion region. We describe the simulation of structures incorporating various kinds of edge termination, including dielectric overlap and ion-implanted guard rings. Dielectric overlap using 5-μm termination of 0.1–0.2-μm-thick SiO₂ increases the breakdown voltage of quasi-vertical diodes with 3-μm GaN epi thickness by a factor of ∼2.7. The use of even one p-type guard ring produces about the same benefit as the optimized dielectric overlap termination.