K. Melichar

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.

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.

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.

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.

Ballistic electron emission spectroscopy/microscopy of self-assembled InAs quantum dots of different sizes embedded in GaAs∕AlGaAs heterostructure

Self-assembled InAs quantum dots embedded in GaAs∕GaAlAs heterostructure were visualized by ballistic electron emission microscopy. The spectroscopic characteristics on individual quantum dots were examined. Quantum dots had images of elliptical shapes. Their length was from about 10to20nm. Below one-electron p1-like state, one-electron and two-electron ground states and excited two-electron states were observed. The Coulomb interaction and exchange energies between two electrons in quantum dots were determined and compared with the previously published theoretical results.

Transport-controlling deep defects in MOVPE grown GaSb

Deep level transient spectroscopy (DLTS) measurements were used to directly observe growth-rate induced defects in MOVPE grown GaSb layers. The DLTS spectra of p–n homojunctions prepared at a growth rate of 40 nm min−1 show a broad minority carrier peak in the temperature range of 190–230 K. The shape of the peak does not correspond to the exponential transient. Assuming a band of localized states with Gaussian distribution, a mean energy of about 0.3 eV above the valence band edge and a characteristic broadening of 75 meV match the measurement. On the other hand, the DLTS spectra of the samples grown at a growth rate of 20 nm min−1 exhibit only a slowly varying background. We conclude that the observed defects are due to the high growth rate of the GaSb layers and control defect-assisted tunnelling previously observed from current–voltage characteristics.

Study of InAs quantum dots in AlGaAs∕GaAs heterostructure by ballistic electron emission microscopy/spectroscopy

Self-assembled InAs quantum dots in GaAs∕GaAlAs structures were examined by ballistic electron emission microscopy/spectroscopy. The studied structures were grown by metal-organic chemical vapor deposition. Quantum dots with an image of elliptical shape were studied. Ballistic current-voltage characteristics through the quantum dot and outside the quantum dot are compared in the voltage range of 0.55–2V. In the voltage range from 0.55to0.8V examples of ballistic characteristics and their derivatives are given. In a detailed study, measurements with 1mV step in the energy range from 0.55to0.63V are presented.

Magneto-photoluminescence study of electronic transitions in InAs/GaAs quantum dot layers

Abstract Magneto-photoluminescence of single- and multi-layered self-organised MOCVD grown InAs quantum dots in GaAs has been investigated at 77 K in magnetic fields up to B=27 T in Faraday configuration. From one up to six peaks are resolved at B=0 T in the photoluminescence spectra when the excitation intensity increases from 10 mW up to 1 W (514.5 nm line of Ar+ laser). Simple one particle Fock–Darwin model of two-dimensional electrons confined in a parabolic well describes satisfactorily the evolution of magneto-photoluminescence only for some peaks. The other peaks exhibit slight decrease in energy with increasing magnetic field (∼5 meV at 27 T).

Lasers with δ InAs layers in GaAs

Abstract Electroluminescence of lasers with different numbers (1, 3, 5, 7) of δ InAs layers in GaAs prepared by Low Pressure Metal–Organic Vapor Phase Epitaxy was investigated in a broad temperature range from 10 to 400 K. The dependence of the electroluminescence spectra on the number of δ InAs layers and on the separation of these δ InAs layers was studied under pulse excitation in a wide range of current densities. Results show that by increasing the number of δ InAs layers and decreasing the distance between these layers it is possible to decrease the lasing emission energy below 1.15 eV. Our δ InAs lasers operate even at temperatures above 100 °C, they exhibit weak temperature dependence of threshold current density with values lower than 0.2 kA cm−2 and their differential quantum efficiency lies between 12 and 18%.