Newly engineered substrates consisting
of semiconductor-on-insulator are gaining much attention as starting materials
for the subsequent transfer of semiconductor nanomembranes via selective
etching of the insulating layer. Germanium-on-insulator (GeOI) substrates are
critically important because of the versatile applications of Ge nanomembranes
(Ge NMs) toward electronic and optoelectronic devices. Among various fabrication
techniques, the Smart-CutTM technique is more attractive than other methods
because a high temperature annealing process can be avoided. Another advantage
of Smart-CutTM is the reusability of the donor Ge wafer. However, it is very
difficult to realize an undamaged Ge wafer because there exists a large
mismatch in the coefficient of thermal expansion among the layers. Although an
undamaged donor Ge wafer is a prerequisite for its reuse, research related to
this issue has not yet been reported. Here we report the fabrication of 4-inch
GeOI substrates using the direct wafer bonding and Smart-CutTM process with a
low thermal budget. In addition, a thermo-mechanical simulation of GeOI was
performed by COMSOL to analyze induced thermal stress in each layer of GeOI.
Crack-free donor Ge wafers were obtained by annealing at 250 °C for 10 h. Raman
spectroscopy and x-ray diffraction (XRD) indicated similarly favorable
crystalline quality of the Ge layer in GeOI compared to that of bulk Ge. In
addition, Ge p-n diodes using transferred Ge NM indicate a clear rectifying
behavior with an on and off current ratio of 500 at ±1 V. This demonstration
offers great promise for high performance transferrable Ge NM-based device
applications.
Source:IOPscience
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