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In-situ desorption mass spectrometry (DMS) tool is used to report monolayer oscillations of the Sb desorption rate during molecular beam epitaxy (MBE) growth of GaSb and GaInSb. Oscillations in the Sb desorption rate appear to be correlated to the variation in the surface-step-density that periodically changes the additional uptake and expulsion of Sb beyond the fixed rate of consumption. This notion is corroborated by comparing the Sb DMS signal to the time derivative of the specular RHEED beam intensity.

We apply the desorption mass spectrometry (DMS) technique and analyze the desorbed Sb species in-situ during MBE growth of mixed As/Sb heterostructures. We demonstrate how DMS is useful in pre-growth calibration of the V/III ratio, the group-III ratio, as well as the Sb-content in quaternary or quinary mixed As/Sb alloys. We also apply DMS to the digital alloy growth method. For demonstration purposes, we start with an un-calibrated MBE system, use the DMS technique to calibrate all of the previously undetermined MBE parameters and grow a ~3.3 µm diode laser heterostructure in only one attempt. The results demonstrate that the DMS technique will allow the MBE to quickly converge toward a set of acceptable growth parameters without the need for ex-situ calibration of alloy composition.

We describe the growth of GaSb-based diode lasers with quinary AlInGaAsSb alloy waveguide/barriers and highly strained InGaAsSb type-I quantum wells, designed to emit at ~3.2 µm at room temperature. To increase the compressive strain in the QWs above the pseudomorphic limit, we employ strain compensation in which the lower portion of the quinary alloy waveguide is slightly arsenic-rich as compared to the lattice-matched composition. Using this scheme, we fabricated a set of laser devices with incrementally increasing compressive strain in the quantum wells. With compressive strain reaching as high as ~2.4%, the device performance corroborates the notion that adding compressive strain in the quantum wells helps improve hole confinement and suppresses carrier leakage during operation near room temperature.

International audience; The growth by molecular-beam epitaxy of novel electrically pumped type-II multi-quantum well (MQW) Sb-based laser diodes in which only the holes are quantum confined was studied. These laser structures were fabricated on (0 0 1) GaSb substrates. In the MQW region, radiative recombinations originate from InGaSb hole wells embedded in InGaAsSb barriers lattice matched to GaSb. Two different laser structures were developed. The first one exhibited a well/barrier periodicity that was too short, which led to a laser emission near 2.65 μm originating from the waveguide rather than from the wells. With an improved well/barrier periodicity, the second structure exhibited laser emission up to 243 K at 2.93 μm in the pulsed regime (200 ns, 5 kHz). In this case, the laser photons were effectively produced by the hole-well active region. A minimum threshold of about 12.8 kA/cm2 at 80 K combined with a T0 around 70 K have been measured from this second structure.

We consider the digital alloy growth of mixed As/Sb layers by molecular beam epitaxy. Using the (InAs)n(GaSb)3n superlattice as an example, we determine an acceptable upper limit to the modulation period before significant deviation from the In0.25Ga0.75As0.25Sb0.75 bandgap occurs. We then consider the digital alloy growth of In0.2Ga0.8AsySb1� y layers on GaSb, and find that the digital alloying technique provides protection against compositional drift in the growth direction due to reduced sensitivity to variations in arsenic-flux and substrate temperature. r 2002 Elsevier Science B.V. All rights reserved.

We have developed an empirical model of AlAsySb1−y composition during molecular beam epitaxy as a function of growth temperature, growth rate, As2-flux, and Sb2-flux, using response surface methodology. In order to facilitate data collection from a large number of experiments, we have applied desorption mass spectroscopy as an in situ measure of alloy composition. A quadratic model is found to fit the data well, identifying trends and several interactions between growth parameters.

We have investigated the effect of a brief As 2 -soak at the GaSb surface on the nature of the InAs-on-GaSb interface. We find that As 2 efficiently removes Sb from GaSb and that a controlled As 2 -soak may be a necessary step in forming a “GaAs-like” interface without structural or optical degradation. We observe that the thickness of the “GaAs-like” interfacial layer and the band-edge transition wavelength in InAs/GaSb superlattices both increase with increasing As 2 -soak duration.

We use the technique of in situ desorption mass spectrometry (DMS) to probe the surface chemistry, and directly observe two phenomena that are responsible for anion intermixing at the InAs-on-GaSb interface: (1) the presence of excess but stable Sb on the GaSb surface that partially incorporates into the InAs layer, and (2) the removal of Sb from within the GaSb layer when the surface is over-exposed to an incident As-flux. We propose and demonstrate that anion intermixing in InAs/GaSb superlattices is minimized when the As-soak time is precisely adjusted to remove the excess surface Sb population while leaving the underlying GaSb layer intact.

Quantitative measurements of Sb surface segregation in pseudomorphic GaAs 0.8 Sb 0.2 layers grown on GaAs (001) using molecular beam epitaxy (MBE) were performed in situ using the line-of-sight mass spectrometry (MS) technique. It was observed that substantial surface accumulation of Sb occurs under normal growth conditions, giving rise to compositional broadening of the GaAsSb on GaAs interface. This compositional grading is found to strongly depend on the growth temperature as well as the presence of Sb at the GaAs film surface prior to the initiation of GaAsSb layer growth. We report the effect to substrate temperature and shutter sequence on the evolution of Sb surface accumulation near the interface and demonstrate that a compositionally abrupt interface can be formed by populating the GaAs surface with an amount of Sb equivalent to that expected on the GaAsSb surface during growth at steady state. Additionally, compositional abruptness at the GaAs on GaAsSb interface can be achieved by a “chemical flashoff” of the surface Sb population during exposure to an incident As 2 flux.

The interaction of a Sb2 molecular beam with the film surface during molecular beam epitaxy (MBE) of GaAs1 − xSbx layers was monitored by a quadrupole mass spectrometer (QMS) positioned in line-of-sight of the substrate. It was observed that the QMS signal from the monomeric Sb-species (massq = 121 or 123 amute) is proportional to the total Sb-flux leaving the film surface within a wide range of temperatures and surface composition. This enabled the accurate determination of the antimony incorporation coefficient, σ(Sb), and consequently the Sb-mole fraction during growth. Due to its applicability in growth conditions where σ(Sb) is less than unity, this compositional monitoring technique expands the practical range of MBE growth parameters for III-As1 − xSbx alloy growth. Real-time in situ control of alloy composition was demonstrated by implementing a feedback control scheme based on the QMS Sb signal. GaAs1 − xSbx alloys in which the Sb-fraction varied in a controlled manner in the direction of growth were deposited.

We report on the implementation of technique of desorption mass spectrometry (DMS) in a real-time feedback loop for continuous monitoring and control of layer composition during molecular beam epitaxy growth of AlGaAs on (001) GaAs at high substrate temperatures. With this technique, the Ga desorption rate Fd(Ga) and thus the composition is monitored continuously and kept at the desired value by adjusting either the substrate heater power or the incident arsenic flux. Composition control by DMS during growth of nominally constant composition layers is found to be superior to that obtained with conventional MBE growth, as indicated by Fd(Ga) versus time profiles and low temperature photoluminescence (PL) results. The ability to produce complex graded structures by DMS control is demonstrated by the growth of nominally parabolic AlGaAs quantum wells, for which photoreflectance and PL results are consistent with the desired structure. The technique is quite general and applicable to many different compounds.