Photoconductivity of InSb/GaAs heterostructures at low temperature

Abstract

We have studied the low-temperature coplanar photoconductivity under pulsed and continuous illumination of n-InSb/GaAs heterostructures grown by metalorganic magnetron sputtering. The large lattice mismatch and the large difference in band gaps give rise respectively to a highly defective region at the interface and a high built-in field. The effect of these factors on the photoconductivity is then a function of the InSb film thickness. For photon energies above the InSb band gap, up to about 0.4 eV, we observe positive photoconductivity due to an increase in the electron density coupled with trapping of the excess minority carriers. As the film thickness is decreased from 2 to 0.2 μm, the photoconductivity gain per absorbed photon decreases and the decay time increases, indicating the presence of trapping or recombination centers near the interface. Illumination with photons of energy greater than 0.4 eV leads to the coexistence of a positive photoconductivity and a very slow transient negative photoconductivity which gives rise to high gains at low modulation frequencies. The negative photoconductivity increases with increasing photon energy and decreasing film thickness. Illumination at 0.9 eV from both sides of the heterostructure shows that the effect is related to diffusion and trapping of hot electrons at the interface. The onset of the saturation of the effect indicates a concentration of electron traps of about 1014 cm−2 at the interface, a value similar to the concentration of edge-type dislocations that predominantly accommodate the lattice mismatch in this heterostructure.

Optical investigation of GaSb thin films grown on GaAs by metalorganic magnetron sputtering

“…The getter-purified high-purity argon was introduced via a mass-flow controller to serve as the carrier gas to control the TMG flow rate. The total gas flow rate was maintained at 30 sccm under a low deposition pressure of ∼0.4 Pa. All growths were carried out in an antimony stabilized regime [20][21][22][23].…”

“…This new growth technique, called metalorganic molecular beam epitaxy (MOMBE) [18] or chemical beam epitaxy (CBE) [19], combines the advantages of MBE and MOVPE, providing stable group V vapor beams for epitaxy. In another approach, we have developed a novel technology of metalorganic magnetron sputtering (MOMS) for the preparation of epitaxial InSb and Sb-based materials and microstructures [20][21][22][23]. Pulsed laser evaporation and epitaxy (PLEE) is another method, which avoids the use of the thermal or vapor sources [24].…”

Time dependence of negative and positive photoconductivity for Si δ-doped AlGaAs/InGaAs/AlGaAs quantum well under various temperatures and various incident photon energies and intensities

“…As mentioned earlier, the NPC observed in n-type InAs NWs [14][15][16][17][18][19][20][21] only occurs when E in is much higher than E g (InAs). Because most of the excess energy (E in −E g ) is gained by the electrons [8], these hot electrons can reach the interface states located above the conduction band minimum and are trapped there. Analogous to the NPC model applied to InAs NWs, the mechanism of the NPC observed in figure 6 with T=180 and 240 K can then be explained as follows.…”

“…The earliest two-level model for the NPC observed in n-type Ge sample [7] proposes that if a localized level located above the Fermi level (E F ) can effectively trap the photo-excited electron for a long enough time, then via a recombination level the photo-excited hole subsequently recombines with electron to reduce the majority carrier concentration, and hence an NPC is triggered. Similar two-level models (one as the trapping center for photo-excited majority and the other one as the recombination center) have been applied to explain the NPC observed in n-InSb layer on semi-insulating GaAs substrate [8] and in two-dimensional electron gas (2DEG) of InAlAs/InGaAs quantum well (QW) heterostructures [9].…”