A method to fabricate GaAs microcavities using only a soft mask with an electrolithographic pattern in an inductively coupled plasma etching is presented. A careful characterization of the fabrication process pinpointing the main routes for a smooth device sidewall is discussed. Using the final recipe, optomechanical microdisk resonators are fabricated. The results show a very high optical quality factors of $Q_\text{opt}>2\times 10^{5}$, among the largest already reported for dry-etching devices. The final devices are also shown to present high mechanical quality factors and an optomechanical vacuum coupling constant of $g_{0}=2\pi\times 13.6$ kHz enabling self-sustainable mechanical oscillations for an optical input power above $1$ mW.

Ar/Cl$_{2}$ etching of GaAs optomechanical microdisks fabricated with positive electroresist

Microstructural and compositional characterisation of electronic materials in support of the development of GaAs, GaN and GaSb based multilayer device structures is described. Electron microscopy techniques employing nanometer and sub-nanometer scale imaging capability of structure and chemistry have been widely used to characterise various aspects of electronic and optoelectronic device structures such as InGaAs quantum dots, InGaAs pseudomorphic (pHEMT) and metamorphic (mHEMT) layers and the ohmic metallisation of GaAs and GaN high electron mobility transistors, nichrome thin film resistors, GaN heteroepitaxy on sapphire and silicon substrates, as well as InAs and GaN nanowires. They also established convergent beam electron diffraction techniques for determination of lattice distortions in III-V compound semiconductors, EBSD for crystalline misorientation studies of GaN epilayers and high-angle annular dark field techniques coupled with digital image analysis for the mapping of composition and strain in the nanometric layered structures. Also, in-situ SEM experiments were performed on ohmic metallisation of pHEMT device structures. The established electron microscopy expertise for electronic materials with demonstrated examples is presented.

Microstructural and compositional characterisation of Electronic Materials

Fabrication of double recess structure by single lithography step using silicon-nitride-assisted process in pseudomorphic HEMTs

An overview of the activities at Gallium Arsenide Enabling TEchnology Centre (GAETEC) at Hyderabad, India is being presented here. GAETEC is a vertically integrated foundry with design, fabrication, assembly, testing, packaging and module-making facilities. The technologies available for production would be described in detail, and mention would be made of those being implemented. Examples of products developed and delivered, and those under development would also be given.

MMIC technology at Gallium Arsenide Enabling Technology Centre

Metal semiconductor field effect transistors (MESFETs) and pseudomorphic high electron mobility transistors (pHEMTs) are used in high frequency microwave applications in monolithic microwave integrated circuits (MMICs) Ground via holes with low inductance to the source electrode of these devices is necessary for high frequency applications and also increasing the packing density of MMICs Dry etching of via holes to the depth of 200 mum in GaAs using photoresist mask is particularly challenging due to its poor selectivity with masking material and the constraints of top and bottom dimensions with smooth sidewall profiles The desired sidewall profile promotes easy coverage of the plated metallisation subsequently Via holes of 200 mum depth with the desired profile and good uniformity over 3" GaAs wafers have been realized with inductively coupled plasma (ICP) etching using chlorine chemistry The near vertical sidewall profile has been achieved by tailoring the photoresist mask profile, photoresist hardening process and the GaAs etching parameters Optical and scanning electron microscopy (SEM) were used to characterize the via profiles

Etching of 200 ϋm deep GaAs via holes with near vertical wall profile using photoresist mask with inductively coupled plasma

We report the fabrication of pseudomorphic high electron mobility transistors (pHEMTs) with engineered recess structure of any width of choice, by a single lithography and etching step with the help of silicon-nitride-assisted process. In this process, a silicon nitride layer is deposited prior to gate lithography. First, the silicon nitride is etched by buffered hydrofluoric acid (BHF) in the gate opening and then selective recessing is performed. The recess base width can be engineered by varying etch time of silicon nitride in BHF. The base width increases linearly with etch time as shown by SEM. We demonstrate that the top photoresist gate opening that decides the gate length is unaffected by any duration of silicon nitride etch time. Thereby, we have engineered the distance from gate edge to n+-GaAs (Lgn+) which decides the gate-to-drain breakdown voltage (BVgd). With this method, BVgd?increased from 12 to 20?V as a function of Lgn+. The electric field distribution across the recess structure has been simulated to interpret this result. Since the high BVgd?of pHEMT is essential for power applications as well as switch applications, this method can be easily adopted even though the corresponding reduction in transconductance and unit current gain cut-off frequency (ft) is only marginal from 375 to 350 mS mm?1?and from 39 to 31?GHz, respectively.

Gate recess structure engineering using silicon-nitride-assisted process for increased breakdown voltage in pseudomorphic HEMTs

Peroral Endoscopic Myotomy has become the preferred therapy for achalasia cardia.An important predictor of the success and safety of this technique remains the correct identification of the Esophago gastric junction and the extent of myotomy. However, this key step may be difficult in a subset of patients. The present case highlights the use of double scope technique to manage such technical issues.

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CG Sridhar

Papers

Etching of 200 ϋm deep GaAs via holes with near vertical wall profile using photoresist mask with inductively coupled plasma

Gate recess structure engineering using silicon-nitride-assisted process for increased breakdown voltage in pseudomorphic HEMTs

Double-Scope peroral endoscopic myotomy technique: Light at the end of the tunnel!

Fabrication of double recess structure by single lithography step using silicon-nitride-assisted process in pseudomorphic HEMTs