High-Performance, Metamorphic In[sub x]Ga[sub 1] - xAs Tunnel Diodes Grown by Molecular Beam Epitaxy.

Thin In[sub x]Ga[sub 1-x]As tunnel junction diodes having compositions from x = 0.53 to 0.75 that span a range of bandgap energies from 0.74 to 0.55 eV, were grown on InP and metamorphic, step-graded In[sub x]Al[sub 1-x]As/InP substrates using molecular beam epitaxy and evaluated in the context of thermophotovoltaic (TPV) applications. Both carbon and beryllium were investigated as acceptor dopants. Metamorphic tunnel diodes with a bandgap of 0.60 eV (x = 0.69) using carbon acceptor doping displayed highest peak current densities, in excess of 5900 A/cm² at a peak voltage of 0.31 V, within a 200 Å total thickness tunnel junction. Identically doped lattice-matched tunnel diodes with a bandgap of 0.74 eV exhibited lower peak current densities of approximately 2200 A/cm² at a higher peak voltage of 0.36 V, consistent with the theoretical bandgap dependence expected for ideal tunnel diodes. Specific resistivities of the 0.60 eV bandgap devices were in the mid-10[sup -5] Ω-cm² range. Together with their 200 Å total thickness, the electrical results make these tunnel junctions promising for TPV applications where low-resistance, thin metamorphic tunnel junctions are desired. [ABSTRACT FROM AUTHOR]