T. Šimeček

Vapor pressure of metal organic precursors

The vapour pressure of four metal organic precursors, diethylzinc, triethylantimony, trimethylgallium and trimethylaluminium, used in the metal organic vapor phase epitaxy processes was measured by a static method in the technologically important temperature range from 238 to 293 K. The experimental data were fitted by the Antoine equation and represent updated values of the present day high-purity materials providing comparison with the previously published data.

Influence of growth rate on charge transport in GaSb homojunctions prepared by metalorganic vapor phase epitaxy

Dark current–voltage (I–V) characteristic measurement in the temperature range from −190 °C to 65 °C was carried out on GaSb p-n homojunctions prepared by low-pressure metalorganic vapor phase epitaxy. It was shown that the charge transport mechanism in these homojunctions is strongly affected by the growth rate of GaSb epitaxial layers. Samples prepared at higher growth rate (40 nm/min.) exhibit an anomalous low-temperature peak of tunneling current which can be explained by the presence of a narrow band of energies due to high concentration of native defects, probably GaSb antisites. The same defect levels are responsible for the generation–recombination current which dominates in these samples at higher temperatures. On the other hand, quite different behavior was found in the case of slowly grown (20 nm/min) samples. At sufficiently low temperatures, a current maximum near 50 mV of forward voltage points out a band-to-band tunneling as a prevailing transport mechanism. With increasing temperature, how...

Photovoltage spectroscopy of InAs/GaAs quantum dot structures

In addition to widely used photoluminescence spectroscopy photovoltaic measurement of quantum dot structures can give complementary information about electron and hole transitions. Structures with self-organized InAs quantum dots in GaAs matrix were grown by the Stranski–Krastanov mechanism using the low pressure metalorganic vapor phase epitaxy technique. Two types of samples were studied, with single and multiple quantum dot layers. We have shown that surface photovoltage spectroscopy can be used for the study of single, as well as multiple quantum dot layer structures.

Study of InAs quantum dots in GaAs prepared on misoriented substrates

Abstract Optical properties of quasi zero-dimensional semiconductor quantum dots were studied by photoluminescence and Raman spectroscopy. The dependence of photoluminescence on substrate orientation and Raman spectra of single and multiple InAs/GaAs quantum dot structures are reported. The samples were grown on (100) oriented GaAs substrates without and with 3° misorientation towards (110) by metal-organic vapor phase epitaxy in the Stranski–Krastanow regime. Strong dependence of photoluminescence properties of the quantum dot structures on substrate misorientation is shown. The InAs-related features are observed in the macro-Raman spectra and micro-Raman spectra. The effects of confinement, alloying and strain on PL and on phonon spectra are discussed.

Broken-gap heterojunction in the p-GaSb-n-InAs1−x Sbx(0≤x≤0.18) system

Epitaxial InAs1−xSbx layers with the Sb content 0≤x≤0.18 were grown by metalorganic vapor phase epitaxy (MOVPE) on p-GaSb and n-InAs substrates. The photoluminescence (PL) spectra of the heterostructures were measured at T=77 K. The experimental PL data were used to study variation of the bandgap as a function of the InAsSb solid solution composition. The energy difference between the GaSb valence band top and the InAs0.82Sb0.18 conduction band bottom was calculated. It was established that GaSb/InAs1− xSbx with 0≤x≤0.18 represents a broken-gap heterojunction of type II.

Low temperature photoluminescence of Ga0.84In0.16As0.22Sb0.78 solid solutions lattice matched to InAs

Low-temperature photoluminescence (PL) study of liquid phase epitaxy grown undoped and Sn doped GaIn0.16As0.22Sb layers lattice matched to InAs is reported. The quaternary solid solutions Ga1−xInxAsySb1−y are promising materials for the fabrication of optoelectronics devices operating in the spectral range 3–5 μm because these alloys can form type II heterojunctions both with staggered and broken-gap alignment. The band structure engineering of these devices requires the knowledge of energy gaps and mechanism of radiative recombination transitions in the forbidden gap of cladding layers. The high quality quaternary GaIn0.16As0.22Sb epitaxial layers with low native defect concentration were grown lattice matched to InAs and their photoluminescence was studied at low temperatures. The emission band related to bound exciton was dominant. While the emission bands associated with the first ionization state of VGaGaSb vacancy-antisite defect with activation energy ΔEA=22 meV and unknown deep defect with ΔEB=46 ...

Electroluminescence in p-InAs/AlSb/InAsSb/AlSb/p(n)-GaSb type II heterostructures with deep quantum wells at the interface

Luminescent characteristics of asymmetric p-InAs/AlSb/InAsSb/AlSb/p-GaSb type II heterostructures with deep quantum wells at the heterointerface are studied. The heterostructures were grown by metalorganic vapor phase epitaxy. Intense positive and negative luminescence was observed in the range of photon energies of 0.3–0.4 eV with a forward and reverse bias, respectively. Dependences of the spectra and intensities for positive and negative luminescence on the pumping current and on the temperature are studied in the range of 77–380 K. It is established that, at a temperature higher than 75°C, intensity of negative luminescence surpasses that of positive luminescence by 60%. The suggested heterostructures can be used as lightemitting diodes (photodiodes) with switched positive and negative luminescence in the mid-IR spectral range of 3–4 μm.

InAs/GaAs lasers with very thin active layer

Abstract InAs/GaAs laser structures based on atomically thin InAs strained quantum wells were prepared by metal–organic vapour phase epitaxy. The dependence of electroluminescence spectra on the thickness, as well as on the number of InAs quantum wells, was studied. The temperature dependence of the mode structure and optical output power were studied in the range from 25 to 100°C. The position of laser emission can be shifted by changing the thickness and the number of InAs active layers from 1.15 to 1.4 eV. Wavelength switching with increasing operating temperature and excitation current was observed.

Photovoltaic detector based on type II p-InAs/AlSb/InAsSb/AlSb/p-GaSb heterostructures with a single quantum well for mid-infrared spectral range

Mid-infrared photovoltaic detector (PD) designed on the base of a type II p-InAs/p-GaSb asymmetric heterostructure with a deep AlSb/InAsSb/AlSb quantum well (QW) at the interface is reported. The heterostructures containing the single QW were grown by LP-MOVPE. Transport, electroluminescent and photoelectrical properties of these structures were investigated. Intense both positive and negative electroluminescence was observed in the spectral range 3-4 µm above room temperature (300-400 K). Spectral response in the mid-infrared range 1.2-3.6 μm was obtained at temperatures T=77-300 K. High quantum efficiency η=0.6-0.7 responsivity Sλ=1.4-1.7 A/W and detectivity Dλ* =3.5×1011 cm Hz1/2w-1 were achieved at 77 K. Such QW PDs are suitable for heterodyne spectroscopy and free space communication using quantum cascade lasers as well as for gas analysis and ecological monitoring applications.

InAs/GaAs multiple quantum dot structures grown by LP-MOVPE

Abstract Structures with self-organised InAs quantum dots in a GaAs matrix were grown by the low pressure metal–organic vapour phase epitaxy (LP-MOVPE) technique. Photoluminescence and atomic force microscopy were used as the main characterisation methods for the growth optimisation. The properties of multiple-stacked quantum dot structures are influenced by the thickness of the GaAs separation layers (spacers) between quantum dot-containing InAs layers, by the InAs layer thickness, by arsine partial pressure during growth, and by group III precursor flow interruption time.