Conduction electrons localized by charged magneto-acceptors A2−^{2-} in GaAs/GaAlAs quantum wells

A variational theory is presented of A$^{1-}$ and A$^{2-}$ centers, i.e. of a negative acceptor ion localizing one and two conduction electrons, respectively, in a GaAs/GaAlAs quantum well in the presence of a magnetic field parallel to the growth direction. A combined effect of the well and magnetic field confines conduction electrons to the proximity of the ion, resulting in discrete repulsive energies above the corresponding Landau levels. The theory is motivated by our experimental magneto-transport results which indicate that, in a heterostructure doped in the GaAs well with Be acceptors, one observes a boil-off effect in which the conduction electrons in the crossed-field configuration are pushed by the Hall electric field from the delocalized Landau states to the localized acceptor states and cease to conduct. A detailed analysis of the transport data shows that, at high magnetic fields, there are almost no conducting electrons left in the sample. It is concluded that one negative acceptor ion localizes up to four conduction electrons.Comment: 8 pages, 5 figure

Verification of band offsets and electron effective masses in GaAsN/GaAs quantum wells : Spectroscopic experiment versus 10-band k.p modeling

Optical transitions in GaAs1-xNx/GaAs quantum wells (QWs) have been probed by two complementary techniques, modulation spectroscopy in a form of photoreflectance and surface photovoltage spectroscopy. Transition energies in QWs of various widths and N contents have been compared with the results of band structure calculations based on the 10-band k.p Hamiltonian. Due to the observation of higher order transitions in the measured spectra, the band gap discontinuities at the GaAsN/GaAs interface and the electron effective masses could be determined, both treated as semi-free parameters to get the best matching between the theoretical and experimental energies. We have obtained the chemical conduction band offset values of 86% for x = 1.2% and 83% for x = 2.2%, respectively. For these determined band offsets, the electron effective masses equal to about 0.09 m(o) in QWs with 1.2% N and 0.15 m(o) for the case of larger N content of 2.2%.Publisher PDFPeer reviewe

Room temperature carrier kinetics in the W-type GaInAsSb/InAs/AlSb quantum well structure emitting in mid-infrared spectral range

Room temperature carrier kinetics has been investigated in the type-II W-design AlSb/InAs/Ga0:80In0:20As0:15Sb0:85/InAs/AlSb quantum well emitting in the mid-infrared spectral range (at 2.54 μm). A timeresolved reflectance technique, employing the non-degenerated pump-probe scheme, has been used as a main experimental tool. Based on that, a primary carrier relaxation time of 2:3 ± 0:2 ps has been found, and attributed to the initial carrier cooling process within the quantum well states, while going towards the ground state via the carrier-optical phonon scattering mechanism. The decay of a quasi-equilibrium carrier population at the quantum well ground states is primarily governed by two relaxation channels: (i) radiative recombination within distribution of spatially separated electrons and holes that occurs in the nanosecond time scale, and (ii) the hole tunnelling out of its confining potential, characterized by a 240 ± 10 ps time constant.Publisher PD

Photoluminescence quenching mechanisms in type II InAs/GaInSb QWs on InAs substrates

We would like to acknowledge the National Science Centre of Poland for support within Grant No. 2014/15/B/ST7/04663.Optical properties of AlSb/InAs/GaInSb/InAs/AlSb quantum wells (QWs) grown on an InAs substrate were investigated from the point of view of room temperature emission in the mid- and long-wavelength infrared ranges. By means of two independent techniques of optical spectroscopy, photoreflectance and temperature-dependent photoluminescence, it was proven that the main process limiting the performance of such InAs substrate-based type II structures is related to the escape of carriers from the hole ground state of the QW. Two nonradiative recombination channels were identified. The main process was attributed to holes tunneling to the valence band of the GaAsSb spacing layer and the second one with trapping of holes by native defects located in the same layer.Publisher PDFPeer reviewe

Wetting layer states of InAs/GaAs self-assembled quantum dot structures. Effect of intermixing and capping layer

The authors present a modulated reflectivity study of the wetting layer (WL) states in mol. beam epitaxy grown InAs/GaAs quantum dot (QD) structures designed to emit light in the 1.3-1.5 micro m range. A high sensitivity of the technique has allowed the observation of all optical transitions in the QD system, including low oscillator strength transitions related to QD ground and excited states, and the ones connected with the WL quantum well (QW). The support of WL content profiles, detd. by transmission electron microscopy, has made it possible to analyze in detail the real WL QW confinement potential which was then used for calcg. the optical transition energies. In spite of a very effective WL QW intermixing, mainly due to the Ga-In exchange process (causing the redn. of the max. indium content in the WL layer to about 35% from nominally deposited InAs), the transition energies remain almost unaffected. The latter effect could be explained in effective mass envelope function calcns. taking into account the intermixing of the QW interfaces described within the diffusion model. We have followed the WL-related transitions of 2 closely spaced QD layers grown at different temps., as a function of the In content in the capping layer. Changing the capping layer from pure GaAs to In0.236Ga0.764As has no significant influence on the compn. profile of the WL itself and the WL QW transitions can be usually interpreted properly when based on the cap-induced modification of the confinement potential within a squarelike QW shape approxn. However, some of the obsd. features could be explained only after taking into consideration the effects of intermixing and InGaAs cap layer decompn. [on SciFinder (R)

Optical and electronic properties of GaAs-based structures with columnar quantum dots

The electronic properties of a structure with columnar quantum dots obtained by close stacking of InAs submonolayers were studied by contactless electroreflectance (CER) and photoluminescence. These dots have an almost ideally rectangular cross section and uniform compn., which is promising for polarization independent gain. After energy level calcns. in the effective mass approxn. using compn. profiles obtained from cross-sectional TEM the part of the CER spectrum related to the 2-dimensional surrounding layer was explained and single heavy-hole-like and light-hole-like transitions related to the columnar dots identified, due to a single electron state confined in a shallow in-plane potential. [on SciFinder (R)

Photoluminescence investigations of 2D hole Landau levels in p-type single Al_{x}Ga_{1-x}As/GaAs heterostructures

We study the energy structure of two-dimensional holes in p-type single Al_{1-x}Ga_{x}As/GaAs heterojunctions under a perpendicular magnetic field. Photoluminescence measurments with low densities of excitation power reveal rich spectra containing both free and bound-carrier transitions. The experimental results are compared with energies of valence-subband Landau levels calculated using a new numerical procedure and a good agreement is achieved. Additional lines observed in the energy range of free-carrier recombinations are attributed to excitonic transitions. We also consider the role of many-body effects in photoluminescence spectra.Comment: 13 pages, 10 figures, accepted to Physical Review

Univalence criteria for linear fractional differential operators associated with a generalized Bessel function

In this paper our aim is to establish some generalizations upon the sufficient conditions for linear fractional differential operators involving the normalized forms of the generalized Bessel functions of the first kind to be univalent in the open unit disk as investigated recently by [{sc E. Deniz, H. Orhan, H.M. Srivastava}, {it Some sufficient conditions for univalence of certain families of integral operators involving generalized Bessel functions}, Taiwanese J. Math. {bf 15} (2011), No. 2, 883-917] and [{sc \u27A. Baricz, B. Frasin}, {it Univalence of integral operators involving Bessel functions}, Appl. Math. Letters {bf 23} (2010), No. 4, 371--376]. Our method uses certain Luke\u27s bounding inequalities for hypergeometric functions ${}_{p+1}F_p$ and ${}_pF_p$