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Fabrication of GaSb microlenses by photo and e-beam lithography and dry etching

Ewa Papis 1Anna Piotrowska 1Eliana Kaminska 1Tadeusz T. Piotrowski 1Krystyna Golaszewska 1Jacek Ratajczak 1Jerzy Katcki 1Jerzy Wrobel 2

1. Institute of Electron Technology (ITE), al. Lotników 32/46, Warszawa 02-668, Poland
2. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland


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 cmHz1/2/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 200oC, 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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Presentation: poster at E-MRS Fall Meeting 2003, Symposium F, by Ewa Papis
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-26 16:39
Revised:   2009-06-08 12:55