Epitaxy of GaSb based structures is of current scientific and technological interest due to their applications as optoelectronic materials in the mid-IR wavelength range, e.g. in photovoltaic and thermophotovoltaic devices. Some designs of such devices require monocrystalline epilayers grown over amorphous films that could further play a role of buried mirrors for photon recycling and/or be used as buried electrical contacts. Thus, there is a widespread interest in developing techniques which allow the growth of high quality semiconductor structures over insulating or electrically conductive films. Epitaxial lateral overgrowth (ELO) might be the technique of choice.

Epitaxial growth by ELO takes place on a substrate covered by a thin amorphous masking film in which a grating of narrow mask-free seeding windows is opened (see [1] for a review). The growth begins exclusively inside the windows, proceeds in a direction normal to the substrate and then continues in lateral direction over the mask. Finally, new epitaxial layer fully covers the masked substrate if growth is long enough for coalescence of adjacent ELO stripes.

In this report our recent results on ELO growth of GaSb layers on (100) GaSb substrates by the liquid phase epitaxy (LPE) are presented. We show that the aspect (width/thickness) ratio of the layers depends strongly on LPE growth conditions. In particular, silicon doping has been found crucial for successful lateral overgrowth of GaSb. The aspect ratio of the layers increases significantly with amount of silicon introduced to the melt up to the limit determined by silicon solubility in the Ga-Sb liquid solution. The results obtained allowed us to optimize the growth procedure, so the GaSb ELO layers with aspect ratio as large as 15 were obtained. Full coverage of the substrate with a new epitaxial layer is obtained when the spacing between the ELO seeding windows is reduced from 500 µm to 100 µm.

Substrates masked with a thin layer of electrically conductive ZrN or insulating SiO₂ were used. Perfect growth selectivity was obtained in both cases. Moreover, a high electrical conductivity of ZrN was preserved after LPE growth that is especially important if the ZrN mask is to be used as buried electrical contact in GaSb devices made of ELO structures.

Crystallographic perfection of the layers was studied by defect selective etching and high resolution x-ray diffraction. We show that substrate dislocations are efficiently blocked by the masking film and laterally overgrown parts of the layers (wings) are nearly dislocation-free despite a high density of dislocations in the substrates used. Also x-ray diffraction reciprocal space maps prove high crystallographic quality of laterally overgrown GaSb.

Downward tilt of ELO wings, the effect commonly observed in many other ELO structures was negligible in the GaSb layers grown on SiO₂-masked substrates. This finding is explained as being due to low LPE growth temperature of GaSb. However, some residual wing tilt was found in the layers grown on ZrN-masked substrates.

Acknowledgements: This work was partially supported by the Polish Committee for Scientific Research under grants 3T08A 021 26 and 3T11B 00 926.

[1] Z.R. Zytkiewicz, Thin Solid Films 412 (2002) 64.

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