MBE growth techniques for InAs-based nBn IR detectors

Abstract

This manuscript describes an investigation of the effects of growth temperature on InAs epitaxial layers and InAs-based nBn detectors grown by molecular beam epitaxy (MBE). The motivation for this work is to improve the overall performance of InAs-based nBn detectors, which depends both on the bulk material quality of the individual device layers, particularly the infrared absorbing layer, as well as on the quality of the layer interfaces, particularly the interface between the absorber and barrier layers. Absorber layer bulk quality and absorber/barrier interface quality are presumably optimized by performing InAs growth at different temperatures, thus the preferred MBE growth strategy is not immediately apparent. InAs epitaxial layers of 2 μm thick are grown at several temperatures ranging from 420 to 490 °C, and are examined by differential interference contrast microscopy, atomic force microscopy, steady-state photoluminescence, and time-resolved photoluminescence measurements. Absorber layers of 2 μm thick in nBn detectors are also grown at the same temperatures as the InAs single layers, and the resulting devices are evaluated on the basis of dark current density. Competitively high InAs material quality and low nBn dark current densities have been achieved across the range of investigated growth temperatures. The material quality of the InAs single epitaxial layers is found to improve monotonically with growth temperature over the investigated range, and likewise, the reverse saturation dark current density of the nBn detectors is found to decrease monotonically with growth temperature. nBn detectors with dark current density within a factor of 5 of Rule 07 are reported. Finally, it is noted that this work uses an InAs growth rate of 0.9 μm/h, whereas many other studies have chosen to use InAs growth rates in the range of 0.2–0.5 μm/h. The results of this study demonstrate that high performance InAs-based detectors can be grown at this more convenient rate.