Ballistic electron emission microscopy spectroscopy study of AlSb and InAs/AlSb superlattice barriers

Abstract

Due to its large band gap, AlSb is often used as a barrier in antimonide heterostructure devices. However, its transport characteristics are not totally clear. We have employed ballistic electron emission microscopy ͑BEEM͒ to directly probe AlSb barriers as well as more complicated structures such as selectively doped n-type InAs/AlSb superlattices. The aforementioned structures were grown by molecular beam epitaxy on GaSb substrates. A 100 Å InAs or 50 Å GaSb capping layer was used to prevent surface oxidation from ex situ processing. Different substrate and capping layer combinations were explored to suppress background current and maximize transport of BEEM current. The samples were finished with a sputter deposited 100 Å metal layer so that the final BEEM structure was of the form of a metal/capping layer/semiconductor. Of note is that we have found that hole current contributed significantly to BEEM noise due to type II band alignment in the antimonide system. BEEM data revealed that the electron barrier height of Al/AlSb centered around 1.17 eV, which was attributed to transport through the conduction band minimum near the AlSb X point. Variation in the BEEM threshold indicated unevenness at the Al/AlSb interface. The metal on semiconductor barrier height was too low for the superlattice to allow consistent probing by BEEM spectroscopy. However, the superlattice BEEM signal was elevated above the background noise after repeated stressing of the metal surface. A BEEM threshold of 0.8 eV was observed for the Au/24 Å period superlattice system after the stress treatment.

Transport properties of Be- and Si-doped AlSb

“…The net carrier concentrations are similar for AlSb͑Be͒ and GaAs͑Be͒, as expected for a nonamphoteric dopant with a unity sticking coefficient. Room-temperature mobilities are indicated next to each data point, and range from 61 cm 2 /V s for (N A ϪN D )ϭ1ϫ10 19 /cm 3 to over 300 cm 2 /V s for samples in the 10 15 -10 16 /cm 3 range. The solid curve is a fit to the data using the functional form ce ϪEa/kT , yielding an activation energy, E a , of 3.21 eV for the Be cell.…”

“…5,[16][17][18][19][20] For example, Chadi calculates a donor level 440 meV above the valence-band maximum ͑VBM͒ of AlSb for the Sb-on-Al antisite (Sb Al ). 16 Shen et al proposed that Al Sb could behave as a deep acceptor or deep donor when there are empty states below the Al Sb energy level.…”

Structural instability and photoacoustic study of AlSb prepared by mechanical alloying

“…Potentially it can be highly resistive and is closely lattice matched to GaSb and therefore has been used as semiinsulating substrate or buffer layer for the epitaxial growth of GaSb [1,2]. AlSb has an indirect band gap with an energy of 1.62 eV [3] and thus is a good candidate for applications such as high-energy photon detectors and as a barrier material to confine electrons in antimonide heterostructure devices [4], in InAs-channel high electron mobility transistors [5,6] and magnetoelectronic hybrid Hall effect devices [7].…”