Nanocontact heteroepitaxy of thin GaSb and AlGaSb films on Si substrates using ultrahigh-density nanodot seeds

A film of GaSb grown epitaxially on a Si substrate is a direct transition semiconductor useful for application as a light source in Si photonics and channel material in next-generation field effect transistors because its energy bandgap is close to the optical fibre communication wavelength and it possesses high carrier mobility. Here, we report a novel method for heteroepitaxial growth of high-quality GaSb/Si films, despite having a lattice mismatch as large as ~ 12%, using elastically strain-relaxed GaSb nanodots with ultrahigh density as seed crystals for film growth. The nanodot seed crystals were grown epitaxially by restricted contact with the Si substrate through nanowindows in an ultrathin SiO2 film on the Si substrate. A light-emitting diode containing GaSb/Si films with a thickness of ~ 90 nm fabricated by this method operated at room temperature. The growth method was also used to fabricate AlGaSb films of high quality. Our method provides a new avenue for heteroepitaxial growth of high-quality film in systems with large lattice mismatch.

Source:IOPscience

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Edge transport in the trivial phase of InAs/GaSb

We present transport and scanning SQUID measurements on InAs/GaSb double quantum wells, a system predicted to be a two-dimensional topological insulator. Top and back gates allow independent control of density and band offset, allowing tuning from the trivial to the topological regime. In the trivial regime, bulk conductivity is quenched but transport persists along the edges, superficially resembling the predicted helical edge-channels in the topological regime. We characterize edge conduction in the trivial regime in a wide variety of sample geometries and measurement configurations, as a function of temperature, magnetic field, and edge length. Despite similarities to studies claiming measurements of helical edge channels, our characterization points to a non-topological origin for these observations.

Source:IOPscience

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Selective and non-selective wet-chemical etchants for GaSb-based materials

A series of wet-chemical etchants for materials lattice-matched to GaSb was investigated. The etch rates for GaSb, AlAsSb, InAsSb and InAs with etch solutions based on KNa–tartaric acid (C4H4KNaO6), citric acid (C6H8O7) and hydrochloric acid were determined and the selectivities for the four different etching solutions are shown. The applicability of the selectivity between GaSb and InAs (respectively InAsSb) with C4H4KNaO6:HCl: H2O2:H2O (selectivity higher than 15:1) and C6H8O7:H2O2 (selectivity around 1:100) is proved by a substrate removal experiment. Also a new etchant for AlAsSb is proposed: HCl:H2O2:H2O etches AlAsSb versus GaSb with a selectivity of 5:1 and the GaSb surface underneath is smooth and without any remaining particles of oxidized aluminium.

Source:IOPscience

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Selective lateral etching of InAs/GaSb tunnel junctions for mid-infrared photonics

We have studied selective etching of the InAs/GaSb tunnel junction (TJ). We show that efficient lateral etching can be achieved with a citric acid:hydrogen peroxide solution. A slight etching anisotropy of around 10% is observed between [1 1 0] and [1 0 0] crystal orientations. The electrical properties of etched TJs do not depend on the diameter of the device which reveals efficient passivation and the absence of current leakage. Specific resistivities in the 2–5 × 10−5 Ω cm−2 range are measured even for diameters compatible with vertical-cavity surface emitting lasers. This work demonstrates that selective lateral etching of an InAs/GaSb tunnel junction is an efficient means to confine the current in GaSb-based heterostructures.

Source:IOPscience

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Very long wavelength infrared focal plane arrays with 50% cutoff wavelength based on type-II InAs/GaSb superlattice

A very long wavelength infrared(VLWIR) focal plane array based on InAs/GaSb type-II super-lattices is demonstrated on a GaSb substrate. A hetero-structure photodiode was grown with a 50% cut-off wavelength of 15.2  m, at 77 K. A 320×256 VLWIR focal plane array with this design was fabricated and characterized. The peak quantum efficiency without an antireflective coating was 25.74% at the reverse bias voltage of −20 mV, yielding a peak specific detectivity of  cmHz W−1. The operability and the uniformity of response were 89% and 83.17%. The noise-equivalent temperatur

Source:IOPscience

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