Development of InSb dry etch for mid-IR applications
We present a new chlorine-free dry etching process which was used to successfully etch indium antimonide grown on gallium arsenide substrates while keeping the substrate temperature below 150°C. By use of a reflowed photoresist mask a sidewall with 60degree positive slope was achieved, whereas a nearly vertical one was obtained when hard masks were used. Long etch tests demonstrated the non-selectivity of the process by etching through the entire multi-layer epitaxial structure. Electrical and optical measurements on devices fabricated both by wet and dry etch techniques provided similar results, proving that the dry etch process does not cause damage to the material. This technique has a great potential to replace the standard wet etching techniques used for fabrication of indium antimonide devices with a non-damaging low temperature plasma process. Display Omitted Chlorine-free low-temperature dry etch of MBE grown InSb on GaAs60° positive sloped or nearly vertical etch depending on maskNon-selective process etching through Insb, GaSb and GaAsLow damage process with potential to replace standard InSb wet etch
Investigation of the Optical Properties of InSb Thin Films Grown on GaAs by Temperature-Dependent Spectroscopic Ellipsometry
InSb thin films were grown on GaAs substrates by metal organic chemical vapor deposition (MOCVD) and investigated by temperature-dependent spectroscopic ellipsometry (TD-SE). The refractive index, extinction coefficient, and dielectric function of the InSb films were extracted. The variation of critical point energies (E1, E1+Δ1, E2, E1'$$ {E}_1^{\hbox{'}} $$) related to the excited state transitions of InSb and the second energy derivatives of the dielectric function at different temperatures showed that the InSb thin film had high electrical and optical stability at the evaluated temperatures. TD-SE analysis revealed a temperature range suitable for the use of InSb/GaAs-based devices. Beyond 250°C, InSb was heavily oxidized to form a thin In-O layer, causing a pronounced change in the optical constants. The results indicated that optimized InSb thin films grown on GaAs by MOCVD possess good optical and structural properties.
Effects of the mineral phase and valence of vanadium on vanadium extraction from stone coal
The influence of roasting on the leaching rate and valence of vanadium was evaluated during vanadium extraction from stone coal. Vanadium in stone coal is hard to be leached and the leaching rate is less than 10% when the raw ore is leached by 4 mol/L H2SO4 at 90°C for 2 h. After the sample is roasted at 900°C for 2 h, the leaching rate of vanadium reaches the maximum, and more than 70% of vanadium can be leached. The crystal of vanadium-bearing mica minerals decomposes and the content of V(V) increases with the rise of roasting temperature from 600 to 900°C, therefore the leaching rate of vanadium increases significantly with the decomposition of the mica minerals. Some new phases, anorthite for example, form when the roasting temperature reaches 1000°C. A part of vanadium may be enwrapped in the sintered materials and newly formed phases, which may impede the oxidation of low valent vanadium and make the leaching rate of vanadium drop dramatically. The leaching rate of vanadium is not only determined by the valence state of vanadium but also controlled by the decomposition of vanadium-bearing minerals and the existence state of vanadium to a large extent.