InAs/Ga1-xInxSb infrared superlattice diodes: correlation between surface morphology and electrical performance

Abstract

The structural properties of InAs/Ga<SUB>1-x</SUB>In<SUB>x</SUB>Sb infrared (IR) superlattice layers grown by MBE on GaSb substrates have been investigated using high-resolution X- ray diffraction, atomic force microscopy (AFM), secondary ion mass spectroscopy and photoluminescence (PL) spectroscopy. Excellent layers could be grown with a residual mismatch below 1 X 10<SUP>-3</SUP> showing interference oscillations in the X-ray diffraction pattern and high PL efficiency. IR-photodiodes processed from such layers show high responsivity and low leakage currents. The influence of n- and p-doping on the PL efficiency of IR superlattices has been investigated, showing a stronger decrease of the PL intensity for n-doping than for p-doping. Growing the IR-SLs with an As/In V/III ratio below 5, defects with a size of about 1 to 5 micrometers in diameter are observed in the AFM scans. The surface morphology between the defects remains perfect. The defects do not significantly affect the X-ray diffraction patterns and the PL intensity. In a minority-carrier-device, such as IR- photodiodes, the defects are associated with defect-assisted tunneling currents leading to a strong degradation of the electrical performance. By optimizing the growth conditions the defect density can be significantly reduced resulting in a surface roughness given by the standard deviation of the measured height profile of the AFM measurement below 0.3 nm leading to excellent device performance.