XeF2 gas-assisted focused-ion-beam etching of InSb quantum wells for rapid prototyping of semiconductor nanodevices

InSb is a III-V narrow-gap semiconductor with properties such as low effective mass, high mobility, and strong spin-orbit coupling making it an ideal material for applications such as spintronics [1] mid-infrared photonics [2], and nanoelectronics [3]. InSb quantum wells can be made by growing an InSb/InAlSb structure on a Ga substrate using molecular beam epitaxy [4]. However, it is notoriously difficult to fabricate nanodevices from InSb/InAlSb quantum wells due to factors such as its low thermal budget [5] and the production of non-volatile by-products in conventional etching processes, leading to unwanted deposition of material onto the material surface [6]. Current wet and dry etching techniques take a long time and require expensive lithography masks to make new devices, slowing the development of optimised nanodevices.

We investigate focused ion beam (FIB) lithography as a ˜rapid prototyping" fabrication technique to create semiconductor nanodevices from InSb quantum wells. FIB methods have the advantage of being relatively quick and ˜masklessâ", making them ideal for use in the research environment as new iterations of device design can be made quickly and different etching chemistries and electrical properties can be tested in-situ [7]. A variety of Xe plasma FIB parameters were tested to optimise the feature resolution and etching quality of milled
trenches at low temperatures. The XeF2 gas-assisted etching process was also studied as an alternative to the Cl2 chemistry that is typically employed for dry etching of InSb. Cross-sections and profiles of the trenches indicate that the XeF2 etch yields superior trench smoothness and mills material from the surface at a much higher rate. This method was also less prone to deposition of unwanted material onto the surface of the sample. This high-resolution fabrication method can be used for the rapid development and optimisation of individual nanoscale devices before mass production.