Semiconductor microlenses fabricated by one-step wet etching

Summary form only given. Microlenses and microlens arrays are critical in interfacing photonic devices such as VCSELs, photodiodes, and eventually in building compact photonic integrated circuits. Among others, refractive microlens formed directly onto semiconductor materials draw much attention because of the ability of high level integration with other semiconductor optoelectronic devices, as well as their large numerical aperture that enhances light capture angle. A number of techniques have been developed to fabricate semiconductor microlenses. One approach involves photoresist reflow followed by reactive-ion etching. However, the earlier techniques require multiple process steps, a high temperature process, and/or expensive processing equipment. We propose and demonstrate a simple one-step wet chemical etching technique, using a diffusion-limited etching method, to fabricate high quality microlenses of GaAs and InP. Previously, the diffusion limited etching technique was successfully used in forming smooth vertical tapers, which were then integrated in InGaAsP laser diodes for adiabatic optical mode transformation.