GaSb and related semiconductors are well recognised for their potential application in mid-infrared optoelectronics and thermophotovoltaics. We have recently demonstrated fabrication of DH InGaAsSb/AlGaAsSb/GaSb mid-IR photodetectors with detectivity ranged from 5x10¹⁰ to 2x10¹¹ cmHz^1/2/W, depending on the active area and cutoff wavelength.
One of the possible way of improving photodetector performance is a monolithical integration of device structure with hemispherical/hyperhemispherical microlenses enabling effective concentration of IR radiation and increasing device detectivity.
In this work we present the results of fabrication lenses arrays in GaSb substrate using both resist reflow/dry etching and binary optics techniques. Photo and electron beam lithography techniques were used to define lenses pattern.
Surface morphology, diameters and shape of the lenses after dry etching were determined by optical microscopy with Nomarski contrast, SEM, and Tencor Alpha-step profilometer.
In the case of the resist reflow technique photoresist cylinders were melt into spherical lenses by heating on a hot plate at temperature over 200^oC, depending on the lens diameter and thickness. In the pattern transfer process the control of the relative etch rates of the photoresist and substrate was critical to achieve the desired microlens properties. The sputter etching in Ar⁺ was chosen to etching refractive microlenses. Binary optics technology requires anisotropy etching with high selectivity between mask and substrate. Reactive ion etching in BCl₃ plasma with RF power of 10W was used to transfer preshaped AZ PF514 electronoresist into GaSb substrate. We have obtained high quality spherical microlens arrays with diameters up to 10μm and circular gratings with 400nm linewidth and 1μm period.

This work is partly supported by the State Committee for Scientific Research under the grant No 4 T11B03922



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