M C Arikan

An analysis of Hall mobility in as-grown and annealed n- and p-type modulation-doped GaInNAs/GaAs quantum wells

In this study, we investigate the effect of annealing and nitrogen amount on electronic transport properties in n- and p-type-doped Ga0.68In0.32NyAs1 − y/GaAs quantum well (QW) structures with y = 0%, 0.9%, 1.2%, 1.7%. The samples are thermal annealed at 700°C for 60 and 600 s, and Hall effect measurements have been performed between 10 and 300 K. Drastic decrease is observed in the electron mobility of n-type N-containing samples due to the possible N-induced scattering mechanisms and increasing effect mass of the alloy. The temperature dependence of electron mobility has an almost temperature insensitive characteristic, whereas for p-type samples hole mobility is decreased drastically at T > 120 K. As N concentration is increased, the hole mobility also increased as a reason of decreasing lattice mismatch. Screening effect of N-related alloy scattering over phonon scattering in n-type samples may be the reason of the temperature-insensitive electron mobility. At low temperature regime, hole mobility is higher than electron mobility by a factor of 3 to 4. However, at high temperatures (T > 120 K), the mobility of p-type samples is restricted by the scattering of the optical phonons. Because the valance band discontinuity is smaller compared to the conduction band, thermionic transport of holes from QW to the barrier material, GaAs, also contributes to the mobility at high temperatures that results in a decrease in mobility. The hole mobility results of as-grown samples do not show a systematic behavior, while annealed samples do, depending on N concentration. Thermal annealing does not show a significant improvement of electron mobility.

Spectral photoconductivity and in-plane photovoltage studies of as-grown and annealed GaInNAs/GaAs and GaInAs/GaAs quantum well structures

We present an investigation of thermal annealing effects on spectral photoconductivity and in-plane photovoltage, at temperatures between 30 K and 300 K, in sequentially grown GaInNAs/GaAs and GaInAs/GaAs quantum well structures. Our results indicate that thermal annealing not only improves the sample quality but also causes the blueshift as commonly observed by other groups in optical studies. We show that the observed anneal-induced blueshift behaviour can be explained in terms of two competing mechanisms: the redistribution of nearest neighbour configuration and the change of quantum well profile. We also show that thermal annealing increases the intensity of photoconductivity signal but reduces the in-plane photovoltage signal drastically.

Influence of nitrogen on hole effective mass and hole mobility in p-type modulation doped GaInNAs/GaAs quantum well structures

Nitrogen dependence of hole effective mass and hole mobility in p-type modulation doped Ga0.68In0.32NyAs1−y/GaAs quantum well structures with y = 0, 0.009, 0.012, 0.017 are investigated using magnetotransport and Hall effect measurements. Observed N-dependent reduction of the hole effective mass is explained by stronger confinement of holes. Hole effective mass is also found to have hole density dependence due to the strain-induced valance band non-parabolicity. A tendency to decrease in hole effective mass upon annealing can be attributed to the reduction of well width and/or decrease in hole density. A significant improvement in low temperature hole mobility is observed after annealing.

Analytic modeling of temperature dependence of 2D carrier mobility in as-grown and annealed GaInNAs/GaAs quantum well structures

Temperature and nitrogen dependence of 2D carrier mobility in as-grown and annealed Ga1−xInxNyAs1−y/GaAs quantum well (QW) structures (x = 0.32; y = 0, 0.009, and 0.012) are investigated. An analytical model that accounts for the most prominent scattering mechanisms is used to explain the characteristic of temperature dependence of the carrier mobility. An expression for alloy scattering-limited mobility in N-related alloys is developed to explain the behavior of hole mobility for N-containing p-type samples. Analytical modeling of temperature dependence of the electron mobility indicates that N-related alloy scattering and interface roughness scattering are the dominant mechanism at the entire temperature range of interest. The temperature insensitivity of the electron mobility is explained in terms of the overriding effect of N-related alloy scattering and high 2D electron density. A deviation between theoretical and experimental electron mobility at low temperatures is observed not to have any dependency on N concentration. We, therefore, suggest that CNM interaction parameter of the band anti-crossing (BAC) model must be defined as temperature dependent in order to explain the observed low temperature characteristics of electron mobility. The hole mobility is mainly restricted by interface roughness and alloy scatterings at temperatures lower than 100 K, whilst high temperature hole mobility is drastically affected from optical phonon scattering. Moreover, the hole mobility at high temperatures exhibits an N-independent characteristic and hole density starts to increase at temperatures above 70 K, which is explained using the concept of parallel conduction. Extraction of the hole density in each transport channel (QW and barrier) by using a simple parallel conduction extraction method (SPCEM) shows that, in p-type samples, low temperature hole mobility takes place in quantum well, while as temperature increases barrier channel also contribute to the hole mobility and becomes dominant at high temperatures. The experimental and calculated Hall mobility results reveal that thermal annealing has decreased interface roughness and alloy scatterings.

Photo-induced transient spectroscopy of defect levels in GaInNAs

The photo-induced transient spectroscopy (PITS) technique was used to investigate the capture and emission dynamics of deep levels in Ga0.8In0.2N0.015As0.985/GaAs and Ga0.8In0.2As/GaAs quantum wells, sequentially grown by molecular beam epitaxy. A broadband white light or a filtered light was used to identify and discriminate the trapping centres present in the sample. Among all the features discovered in this experiment two PITS peaks, showing activation energies of 160 and 330 meV, have been associated with deep levels in GaInNAs.

High carrier concentration induced effects on the bowing parameter and the temperature dependence of the band gap of GaxIn1−xN

The influence of intrinsic carrier concentration on the compositional and temperature dependence of the bandgap of GaxIn1−xN is investigated in nominally undoped samples with Ga fractions of x = 0.019, 0.062, 0.324, 0.52, and 0.56. Hall Effect results show that the free carrier density has a very weak temperature dependence and increases about a factor of 4, when the Ga composition increases from x = 0.019 to 0.56. The photoluminescence (PL) peak energy has also weak temperature dependence shifting to higher energies and the PL line shape becomes increasingly asymmetrical and broadens with increasing Ga composition. The observed characteristics of the PL spectra are explained in terms of the transitions from free electron to localized tail states and the high electron density induced many-body effects. The bowing parameter of GaxIn1−xN is obtained from the raw PL data as 2.5 eV. However, when the high carrier density induced effects are taken into account, it increases by about 14% to 2.9 eV. Furthermore,...

The orbit centre dependence of the energy levels in a single quantum well under external tilted magnetic and electric fields

The analytical solutions of the Schrodinger equation for a square well system subjected to an externally applied electric field in the growth direction and an externally applied tilted magnetic field are obtained and the results are discussed. The dependence of the energy spectrum of the system on the external electric fields as a function of the orbit centre is also discussed.

Hot Electron Light Emitting Semiconductor Heterojunction Devices (Hellish) — Type — 1 and Type — 2

One of the draw-backs of the conventional light emitters appears to be that the light emission is confined to a small region of the facets of the devices1. Thus, the compatibility in generic integration technology remains a problem. The research on simple devices that emit light from the surface with good control of wavelength tunability, and which can be fabricated in large scale 2- dimensional arrays has been largely stimulated by potential applications in optical signal processing. One possible candidate for such a simple functional device is the light emitting charge injection transistor (CHINT) 2. Another light emitter, HELLISH-1 (Hot Electron Light Emission and Lasing in Semiconductor Heterostructures) has been proposed by us3–5. In this paper we present a novel surface emitting device, HELLISH-2 and demonstrate its operation with a simple model. We also report the results of our recent studies on a heavily p-n doped HELLISH-1 device.

Effects of an intense, high-frequency laser field on bound states in Ga1 − xInxNyAs1 − y/GaAs double quantum well

Within the envelope function approach and the effective-mass approximation, we have investigated theoretically the effect of an intense, high-frequency laser field on the bound states in a GaxIn1 − xNyAs1 − y/GaAs double quantum well for different nitrogen and indium mole concentrations. The laser-dressed potential, bound states, and squared wave functions related to these bound states in Ga1 − xInxNyAs1 − y/GaAs double quantum well are investigated as a function of the position and laser-dressing parameter. Our numerical results show that both intense laser field and nitrogen (indium) incorporation into the GaInNAs have strong influences on carrier localization.

Photoinduced transient spectroscopy of deep levels in GaAs/Ga1−xAlxAs multiple quantum wells

The capture and emission dynamics of deep levels in GaAs/Ga1−xAlxAs multiple quantum well structures are investigated by using the photoinduced transient spectroscopy technique. In nominally undoped samples three trapping levels with activation energies in the range between 0.4 and 0.8 eV are observed. These are compared with the observations based on other conventional techniques. Large capture cross sections associated with the trapping centers implies that the presence of these can be detrimental for the high speed operation of optoelectronic devices based on GaAs/Ga1−xAlxAs quantum well structures.