ZnBeTe Buffer Layers for AlGaAs-GaAs Quantum Well Solar Cell Junctions Epitaxially Integrated on Silicon

Epitaxial growth of beryllium telluride BeTe and Zn
_0.06
Be
_0.94
Te by MBE on silicon was investigated as an approach towards multijunction solar cells. The good crystal properties, optical transparency, thermal stability and high p-type doping levels are positive attributes for a buffer layer for further growth of top solar cell junctions. AlGaAs-GaAs quantum well junctions were grown with close lattice matching to a Zn
_0.06
Be
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Te buffer. AlGaAs layers on ZnBeTe were metastable, with thin layers roughening under growth at normal growth temperatures and rates. Planar growth was done using a low temperature growth initiation until a stable film thickness of 700 Aring. High doping of p-BeTe (2e19 /cm2) was achieved using nitrogen plasma. Electrical transport properties of p-i-n junctions under illumination were measured, integrated to silicon via an n+Si/p+Zn
_0.06
Be
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Te tunnel junction. One sun photocurrent was up to J
_SC
=7.9 mA/cm
²
in a 1.5 eV Al
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Ga
_0.94
As-GaAs junction