We present a study of electron gas properties in InAs nanowires determined by interaction between nanowire geometry, doping and surface states. The electron gas density and space distribution are calculated via self-consistent solution of coupled Schroedinger and Poisson equations in the nanowires with a hexagonal cross-section. We show that the density of surface states and the nanowire width define the spatial distribution of the electrons. Three configurations can be distinguished, namely the electrons are localized in the center of the wire, or they are arranged in a uniform tubular distribution, or finally in a tubular distribution with additional electron accumulation at the corners of the nanowire. The latter one is dominating for most experimentally obtained nanowires. N-type doping partly suppresses electron accumulation at the nanowire corners. The electron density calculated for both, various nanowire widths and different positions of the Fermi level at the nanowire surface, is compared with the experimental data for intrinsic InAs nanowires. Suitable agreement is obtained by assuming a Fermi level pinning at 60 to 100 meV above the conduction band edge, leading to a tubular electron distribution with accumulation along the corners of the nanowire.Electron and hole gas in semiconductor nanowires of the sizes compared to the de Broglie wavelength is a fascinating object since its properties are determined by quantum-mechanical effects. Moreover, III/V semiconductors offer a wide range of opportunities to change the nanowire material composition, geometry and heterostructure design. This, in turn has a lot of implications, namely nanowires act as a test bed for detailed study of fundamental physics in low-dimensional systems as well as a perspective platform for numerous applications in nanoelectronics, optoelectronics, and spintronics 1-4 . The quantization in the potential landscape of a nanowire is ruled by both the Schroedinger and Poisson equations with appropriate boundary conditions at the surface. Thus, the state of a nanowire surface might strongly govern both charge carrier distribution and density within a nanowire. This apparently holds for InAs surface which is known for its high density of surface states in particular after exposure to air [5][6][7][8][9][10][11][12][13] . It is believed that due to the dominating donor-type surface states, supplying electrons to nanowire body, even intrinsic InAs nanowires have high n-type conductivity without additional doping [14][15][16][17][18][19][20][21][22][23][24] . In addition, low contact resistance of InAs nanowires 25 is another indication for the formation of an electron accumulation layer at the nanowire surface. It is natural to expect that the electron gas formed in InAs nanowires due to the surface states would possess different features depending on the surface states and the nanowire diameter 14,23,[26][27][28][29][30][31][32][33] . So far there exist several studies of electron and hole gas properties in core-shell nanowires, i.e. nano...

Using a Monte Carlo (MC) technique, we performed numerical modelling of the kinetic segregation effect during epitaxial growth of a heterostructure containing an In c Ga 1−c As quantum well (QW) surrounded by two GaAs barriers. The growth occurs in the direction coinciding with or slightly tilted from [0 0 1]. The model of growth kinetics takes into account the effect of pseudomorphic deformation of the underlying atomic layers onto the activation energy of adatom diffusion in the growing monolayer. It influences the surface segregation of In atoms and affects the QW shape. Within the effective mass approximation, the dependence of the lowest electron-hole transition energy on the degree of In/Ga segregation (in turn, depending upon the growth conditions and substrate tilting angle) was calculated. The calculations were performed using the composition profiles obtained from the MC modelling and taking into account the corresponding distribution of the elastic strain. The results show that the segregation effect leads to a considerable blue shift and broadening of the QW photoluminescence (PL) peak which increase for higher growth temperatures and lower values of the total cation flux from the gas phase onto the growing surface. Growth on vicinal substrates leads to a reduction of the PL peak broadening.

No abstract

No abstract