InGaP/GaAs shadow-mask for optoelectronic integration and MBE regrowth

The epitaxial shadow mask (ESM) MBE technique has proven to yield excellent device structures with highly selective contacts. The epitaxial mask used for the ESM-MBE technique consists of a (7-8 mu m) AlGaAs-layer capped by approximately 1 mu m GaAs. These layers are lithographically patterned for the desired design. Selective etchants are used to achieve the undercut in the AlGaAs-layer. After the (re)growth, these layers have to be removed completely to get access to the grown devices. We now demonstrate a new epitaxial mask design which allows the monolithic integration of ESM-MBE grown devices with devices which are still included in the shadow mask during a first epitaxy. This demands a high bi-directional selectivity of etchants, as well as an Al-free mask layer to prevent degradation problems during the processing. The lattice matched InGaP/GaAs material system (grown by LP-MOVPE) meets all these requirements (even though a thick InGaP layer has to placed on top of the mask). This is shown by a monolithically integrated version of an electro-optical n-i-p-i modulator (regrown in the mask windows) and an opto-electrical receiver, which was grown as part of the mask layers, to an all-optical smart pixel device. The receiver component, a photoconductive pinFET switch, exhibited state-of-the-art performance, e.g. a leakage current of less than 10 pA (-5 V) and a high channel conductance modulation of 10(5). (C) 1998 Elsevier Science B.V. All rights reserved.