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
A new monolithic approach for mid-IR focal plane arrays
Antimonide-based photodetectors have recently been grown on a GaAs substrate by molecular beam epitaxy (MBE) and reported to have comparable performance to the devices grown on more expensive InSb and GaSb substrates. We demonstrated that GaAs, in addition to providing a cost saving substrate for antimonide-based semiconductor growth, can be used as a functional material to fabricate transistors and realize addressing circuits for the heterogeneously grown photodetectors. Based on co-integration of a GaAs MESFET with an InSb photodiode, we recently reported the first demonstration of a switchable and mid-IR sensible photo-pixel on a GaAs substrate that is suitable for large-scale integration into a focal plane array. In this work we report on the fabrication steps that we had to develop to deliver the integrated photo-pixel. Various highly controllable etch processes, both wet and dry etch based, were established for distinct material layers. Moreover, in order to avoid thermally-induced damage to the InSb detectors, a low temperature annealed Ohmic contact was used, and the processing temperature never exceeded 180 °C. Furthermore, since there is a considerable etch step (> 6 μm) that metal must straddle in order to interconnect the fabricated devices, we developed an intermediate step using polyimide to provide a smoothing section between the lower MESFET and upper photodiode regions of the device. This heterogeneous technology creates great potential to realize a new type of monolithic focal plane array of addressable pixels for imaging in the medium wavelength infrared range without the need for flip-chip bonding to a CMOS readout chip.
Thermodynamics on the Carbochlorination of Titanium-bearing Ores
The equilibrium compositions of the multi-component, multi-phase and multi-reaction system of carbochlorination of titanium-bearing ores are calculated with HSC, a computational chemistry software. The thermodynamic equilibrium calculation of the reaction system shows that a complete conversion of titanium-bearing ores is feasible at a temperature near 200oC. At temperatures ranging from 800 to 1600oC, the products of the reaction system are all in gaseous phase. Thermodynamic analysis accords with the industrial practice. The simulated results provide reasonable scientific basis for improving suitable technological conditions of the carbochlorination reduction.