Delta-doped GaAs Research Articles

Effects of doping concentrations and position-dependent mass on the nonlinear optical properties of asymmetric double delta-doped GaAs quantum wells

Effects of doping concentrations and position-dependent mass on the nonlinear optical properties of asymmetric double delta-doped GaAs quantum wells

Effects of hydrostatic pressure, temperature, and position-dependent mass on the nonlinear optical properties of triple delta-doped GaAs quantum well

In this study, we thoroughly investigate the impacts of hydrostatic pressure, temperature, and position-dependent mass (PDM) on the nonlinear optical properties of asymmetric triple δ-doped GaAs quantum wells. Our analysis covers total optical absorption coefficients, relative refractive index changes, nonlinear optical rectification, second harmonic generation, and third harmonic generation. Initially, we employ PDM to solve the time-independent Schrödinger equation using the diagonalization method under effective mass and parabolic band approaches, considering pressure and temperature dependencies. Utilizing the first four energy eigenvalues and eigenfunctions, we apply the compact density matrix method to compute the system’s nonlinear optical properties numerically. The results indicate a shift in optical property peak positions toward lower (higher) energy spectra with increasing hydrostatic pressure (temperature). Furthermore, the influence of PDM shifts the system’s optical properties toward the higher energy spectrum, resembling the effect of temperature. From an experimental and theoretical perspective, one of the topics that researchers work on most is GaAs-based δ-doped systems (δ-doped heterojunction bipolar transistors, δ-doped field effect transistors, δ-multiple independent gate field effect transistors, etc.). We believe these findings will provide valuable insights for the researchers involved in GaAs-based δ-doped optoelectronic device design.

Microscopic insights into metal diffusion and ohmic contact formation in delta-doped GaAs/(Al,Ga)As core/shell nanowires

Semiconductor nanowires (NWs) are promising candidates for use in electronic and optoelectronic applications, offering numerous advantages over their thin film counterparts. Their performance relies heavily on the quality of the contacts to the NW, which should exhibit ohmic behavior with low resistance and should be formed in a reproducible manner. In the case of heterostructure NWs for high-mobility applications that host a two-dimensional electron gas, ohmic contacts are particularly challenging to implement since the NW core constituting the conduction channel is away from the NW surface. We investigated contact formation to modulation-doped GaAs/(Al,Ga)As core/shell NWs using scanning transmission electron microscopy, energy dispersive x-ray spectroscopy and electron tomography to correlate microstructure, diffusion profile and chemical composition of the NW contact region with the current–voltage (I–V) characteristics of the contacted NWs. Our results illustrate how diffusion, alloying and phase formation processes essential to the effective formation of ohmic contacts are more intricate than in planar layers, leading to reproducibility challenges even when the processing conditions are the same. We demonstrate that the NW geometry plays a crucial role in the creation of good contacts. Both ohmic and rectifying contacts were obtained under nominally identical processing conditions. Furthermore, the presence of Ge in the NW core, in the absence of Au and Ni, was found as the key factor leading to ohmic contacts. The analysis contributes to the current understanding of ohmic contact formation to heterostructure core/shell NWs offering pathways to enhance the reproducibility and further optimization of such NW contacts.

Thermal degradation comparison of delta-doped GaAs tunnel junctions using Si and Te n-type dopants

Tunnel junctions (TJs) are essential for high-performance multijunction solar cells to act as transparent low resistance paths for carriers to travel between adjacent cells. However, TJs typically exhibit highly degraded tunneling performance due to unwanted dopant out-diffusion during top cell growth. In this study, GaAs TJs with Si and Te delta-doping (δ-doping) were grown via solid source molecular beam epitaxy to investigate the tunneling performance and thermal stability. While Si δ-doped TJs exhibited typical tunneling characteristics with an Esaki peak current density of 173 A/cm2, Te δ-doped TJs revealed 1.5 A/cm2 at Vbias = 100 mV without negative resistance. It was found that the performance degradation after annealing at 600 °C for 90 min was significantly higher for TJs with Si δ-doping than for Te. Secondary ion mass spectroscopy measurements reveal that Te shows no clear signs of dopant diffusion while Si exhibited significant out-diffusion in the active TJ layer after thermal annealing. The superior thermal stability of Te compared to Si proves to be advantageous as an alternative n-type dopant for high temperature and long duration grown multi-junction solar cells.

Role of resident electrons in the manifestation of a spin polarization memory effect in Mn delta-doped GaAs heterostructures

The spin-memory effect in the GaAs / InGaAs heterostructures with $\delta$<Mn> layer in GaAs barrier have been investigated. The effect consists in spin polarization of Mn atoms due to interaction with photogenerated spin-polarized holes. The investigation of the effect was carried out by analyzing the polarization of the probe photoluminescence pulse in the pump-probe technique. It was shown that the circular polarization degree of probe pulse generated photoluminescence is strongly affected by the interaction of hole spins with spins of Mn atoms polarized by the pump pulse. The latter leads to decrease of circular polarization degree as compared with single pulse excitation ($\delta P$ effect). The amplitude of $\delta P$-effect is most strongly affected by the concentration of resident electrons in the quantum well which is believed to be due the specific compliance with selection rules for optical transition with the participation of unpolarized resident electrons. The rest of the sample's parameters including the spatial separation between $\delta$<Mn> layer and InGaAs quantum well ($d_s$) have a minor effect on the $\delta P$ value which leads to a paradoxical situation of decreasing $\delta P$-effect with the decrease of $d_s$. The proposed experimental technique consisting in creating the significant concentration of resident electrons in the QW may serve as a reliable photoluminescence method determining the strength of this effect as well as the Mn spin relaxation time in a particular nanostructure.

Hydrostatic pressure and interlayer distance effects on non-linear optical proprieties in n-type double delta-doped GaAs quantum wells

Within the framework of the Thomas-Fermi theory, the electronic structure and the nonlinear optical properties in n-type GaAs double delta-doped quantum wells where determined. In particular, was studied the effects of the distance between the doping layers and the hydrostatic pressure on the absorption coefficient and the change in the refractive index. It was found that the interlayer distance has an important effect on potential geometry, while the pressure lowers the bottom of potential. It was found that the influence of the interlayer distance (hydrostatic pressure) generates a red-shift (blue-shift) on the absorption peak and the refractive index change node. The results indicate that the optoelectronic properties in small interlayer distances (25–50 Å) show a high sensitivity to the changes of hydrostatic pressure, whereas for distances larger than 100 Å the effects of hydrostatic pressure are unimportant for the 1-0 transition. On the far-infrared regime, the effects of these parameters can be applied to tuning the position and amplitude of the resonant optical signals.

Enhanced Spontaneous Emission Rates for Single Isoelectronic Luminescence Centers in Photonic Crystal Cavities

Purcell effect enhancement of spontaneous emission rates is demonstrated for isoelectronic trap single-photon emitters. Two-dimensional photonic crystal slabs with L3 defects were fabricated in nitrogen delta-doped GaAs. Photoluminescence spectra of each photonic crystal cavity had a series of sharp and bright lines arising from individual nitrogen luminescence centers, which was confirmed by Hanbury-Brown and Twiss measurements. The emission rates of these lines depended on cavity detuning, indicating a resonant character of the enhancement. The observed emission lifetime in the cavity was 400 ps, which would be the shortest lifetime reported so far for luminescence centers in GaAs.

Hydrostatic Pressure and Temperature Effect on the Electron-Related Optical Responses in Symmetric and Asymmetric n-Type Double Delta-Doped GaAs Quantum Well Under Terahertz Laser Field

The effects of non-resonant intense laser fields on the intersubband-related light absorption and relative refractive index change coefficients in symmetric and asymmetric n-type double $$\delta$$ -doped GaAs quantum wells are investigated. Systems are assumed to be also under the influence of hydrostatic pressure and the change of temperature. The single band effective-mass and envelope function approximations, together with analytical expressions for the linear and third-order nonlinear optical coefficients are used as theoretical tools. According to the numerical outcome, the nonlinear optical response is significantly affected by the intense non-resonant laser radiation, as a result of the associated distortion of conduction band energy profiles. For instance, it is revealed there is a laser-induced transition of the confining potential from double-delta geometry to single-triangular-like shape. Given the additional variations associated with the application of hydrostatic pressure and temperature, all these external probes could be used to control and suitablly tune the electronic and optical properties of GaAs n-type double $$\delta$$ -doped GaAs quantum wells.

Detailed analysis and performance limiting mechanism of Si delta-doped GaAs tunnel diode grown by MBE

High-performance GaAs tunnel diodes (TDs) are fabricated by using Si delta-doping technique. The GaAs TDs exhibited a high peak tunnel-current density of 2,735 A/cm2 and low specific resistivity of 1.46 × 10−4 Ω·cm2. However, the performance of the GaAs TDs deteriorated once the amount of Si delta doping exceeded a certain limit, which has been rarely reported elsewhere. Detailed analyses and numerical simulations of GaAs TDs with various amounts of Si delta doping prove that Si amphoteric behavior governs the performance limit. GaAs TDs with precisely controlled Si delta doping are suitable for cutting-edge tandem solar cell applications.

The Effect of the Composition of a Carrier Gas during the Growth of a Mn delta-Layer on the Electrical and Magnetic Properties of GaAs Structures

The effect of the arsine content (from 0 to 8 μmol), supplied to a reactor together with hydrogen, on the formation of delta-doped gallium-arsenide structures by the pulsed laser sputtering of a Mn target is investigated. It is found that an arsine molar fraction of ~2.5 μmol in the reactor atmosphere during the formation of a Mn delta-doped GaAs layer allows one to obtain single-crystal epitaxial structures with the lowest layer resistance and a ferromagnetic-paramagnetic phase transition temperature of about 40 K. Increasing the arsine content to 8 μmol or the absence of arsine in a hydrogen flow leads to a significant increase in the layer resistance in the temperature range below 150 K and a decrease in the Curie temperature. In the first case, this may be due to partial compensation of the hole conductivity by donor-type defects formed as a result of an excess of arsenic on the growing surface (arsenic atoms in Ga positions or in interstitial positions). In the second case, when no arsine is supplied to the reactor, the growth surface is likely to be enriched with gallium atoms, which makes the incorporation of Mn into the Ga sublattice difficult.

Влияние состава газа-носителя в процессе роста дельта-слоя Mn на электрические и магнитные свойства GaAs-структур

AbstractThe effect of the arsine content (from 0 to 8 μmol), supplied to a reactor together with hydrogen, on the formation of delta-doped gallium-arsenide structures by the pulsed laser sputtering of a Mn target is investigated. It is found that an arsine molar fraction of ~2.5 μmol in the reactor atmosphere during the formation of a Mn delta-doped GaAs layer allows one to obtain single-crystal epitaxial structures with the lowest layer resistance and a ferromagnetic-paramagnetic phase transition temperature of about 40 K. Increasing the arsine content to 8 μmol or the absence of arsine in a hydrogen flow leads to a significant increase in the layer resistance in the temperature range below 150 K and a decrease in the Curie temperature. In the first case, this may be due to partial compensation of the hole conductivity by donor-type defects formed as a result of an excess of arsenic on the growing surface (arsenic atoms in Ga positions or in interstitial positions). In the second case, when no arsine is supplied to the reactor, the growth surface is likely to be enriched with gallium atoms, which makes the incorporation of Mn into the Ga sublattice difficult.

Morphological and chemical instabilities of nitrogen delta-doped GaAs/(Al, Ga)As quantum wells

The microstructure and the element distribution across tensile-strained nitrogen δ-doped GaAs/(Al,Ga)As quantum wells (QW) are investigated by transmission electron microscopy. We find that the nitrogen sub-monolayer insertion results in a several monolayer thick Ga(As,N) layer with thickness and lateral composition fluctuations. The thickness and composition fluctuations are not arbitrary, but they are anticorrelated, i.e., the Ga(As,N) layer is thinner in areas of higher nitrogen content and vice versa. Thus, regardless of the specific position along the QW, the amount of incorporated nitrogen remains constant and close to its nominal value. The increase in the nitrogen content at the insertion promotes an anisotropic shape transition towards highly faceted three-dimensional structures. Our experimental observations indicate that the two-dimensional to three-dimensional morphological transition is determined by intrinsic factors associated with the different Ga-N and Ga-As bonds and hence occurs regardless of the epitaxial strain state of the layers.

Selfsimilar analysis of n-type delta-doped quasiregular GaAs quantum wells

We study the electronic structure of n-type delta-doped quantum wells in GaAs in which the multiple well system is built according to the Fibonacci sequence. The building blocks A and B correspond to delta-doped wells with impurities densities n2DA and n2DB, and the same well width. The Thomas-Fermi approximation, the semi-empirical sp3s* tight-binding model including spin, the Surface Green Function Matching method and the Transfer Matrix approach were implemented to obtain the confining potential, the electronic structure and the selfsimilarity of the spectrum. The fragmentation of the electronic spectra is observed whenever the building blocks A and B interact and it increases as the difference of impurities density between A and B increases as well. The wave function of the first state of the fragmented bands presents critical characteristics, this is, it is not a localized state nor a extended one as well as it has selfsimilar features. So, the quasiregular characteristics are preserved irrespective of the complexity of the system and can affect the performance of devices based on these structures

Single-photon generation from a nitrogen impurity center in GaAs

We have demonstrated single-photon emission from a nitrogen luminescence center in GaAs. An inhomogeneously broadened luminescence band formed by localized centers was observed in the spectral range from 1480 meV to 1510 meV at 5 K in nitrogen delta-doped GaAs. Optical properties of the individual centers were investigated by steady-state and time-resolved micro photoluminescence. We have found that a bright luminescence center emits single photons with a radiative lifetime of 650 ps, which is much shorter than the lifetime of NN pairs in previous reports.

Photoreflectance spectroscopy of delta-doped GaAs layers

Delta-doped GaAs layers have been studied by photoreflectance spectroscopy. The built-in electric fields and interband transition energies in the semiconductor structure have been evaluated from analysis of Franz-Keldysh oscillations. The delta-doped region is found to have an increased interband transition energy, which is interpreted in terms of the Burstein-Moss effect and carrier photogeneration.

Crossover from negative to positive magnetoresistance in a Si delta-doped GaAs single quantum well

Abstract We have performed magnetoresistance measurements on a Si delta-doped GaAs single quantum well. With increasing temperature T , a crossover from negative magnetoresistance (NMR) to positive magnetoresistance (PMR) can be observed. Our experimental results suggest that such a crossover corresponds to a transition from variable range hopping regime to activated electron transport. This is also consistent with the measured non-monotonic carrier density dependence on T .

Growth and Characterization of C60/GaAs Interfaces and C60 doped GaAs

Intensity oscillations of reflection high-energy electron diffraction are observed during epitaxial growth of a C60 layer on GaAs substrates. The frequencies of the oscillations coincide well with the growth rates of C60 layers, suggesting that C60 layers grow by layer-by-layer growth mode. C60 uniformly doped and delta-doped GaAs layers are grown by migration enhanced epitaxy method. C60 uniformly doped GaAs layers show highly resistive characteristics, suggesting that C60 molecules cannot be decomposed into isolated C atoms. Electrochemical capacitance-voltage profiles of C60 delta-doped GaAs layers suggest that C60 molecules in GaAs lattice produce deep electron traps which can be charged or discharged by applied electrical fields.

Photoluminescence from single isoelectronic traps in nitrogen delta-doped GaAs grown on GaAs(1 1 1)A

We have studied photoluminescence (PL) observed from single isoelectronic traps formed by nitrogen pairs in nitrogen δ-doped GaAs layers grown on GaAs(1 1 1)A substrates. The PL was composed of a single peak with a narrow linewidth of ∼80 μeV. Polarized PL measurements confirmed that the emission from single isoelectronic traps in nitrogen δ-doped GaAs(1 1 1) is unpolarized irrespective of nitrogen pair arrangements. These results can be explained by in-plane isotropy of the samples, which is consistent with the symmetrical property of GaAs(1 1 1), and demonstrate that utilizing (1 1 1) substrate is an effective means for obtaining unpolarized single photons, which are desirable for the application to quantum cryptography.

Wide frequency band detection on laterally constricted GaAs structures having nanometric heavily doped layers

Experimental results of planar asymmetrically and symmetrically shaped hot carrier microwave detectors having five delta-doped GaAs layers are presented. The results are compared with the detectors having the same geometrical shape but only homogeneously doped GaAs layer of submicrometric thickness. DC measurements showed that the structure with delta-doped layers had slightly lower resistance than the detector with homogeneously doped layer due to higher carrier mobility in the delta-doped structure. Increase in carrier mobility corresponded to higher voltage sensitivity, which is essential parameter of a microwave detector. Voltage power characteristics of the detectors of both types were linear up to 10 mW of microwave power, whereas at higher powers they became super-linear or sub-linear with the following change in polarity of the detected voltage. Distinctive dependence of the detected voltage on microwave power at strong electric field is attributed to intervalley transfer of charge carriers. Experimental results of voltage sensitivity in microwave frequency range showed that drop-off of sensitivity going from Ka range to W range for both types of detectors is not larger than 3 dB, suggesting their use for wide frequency detection.

AlGaAs/GaAs heterojunction phototransistor with a double delta-doped base grown by AP MOVPE

Heterojunction bipolar phototransistors (HPTs), based on GaAs technology, are widely used in the optoelectronic-integrated circuit (OEIC) [H.T. Lin, D.H. Rich, A. Larsson, J. Appl. Phys. 79 (1996) 8015 [1]; Lin Chien-chung, M. Wayne, J.S. Harris Jr., F. Sugihwo, Appl. Phys. Lett. 76 (2000) 1188 [2]]. They exhibit a large optical gain and a negligible noise level at low bias voltages. The presented work describes the fabrication and device characteristics of n–p–n AlGaAs/GaAs heterojunction phototransistor with a double Zn delta-doped GaAs base region (2δ-Zn-AlGaAs/GaAs HPT). Such construction of the transistor allows to obtain higher current gain and lower power consumption. The electrical and optical properties of the epitaxial HPT structure were examined using capacitance–voltage (EC– V) measurements, photovoltage, photocurrent and micro-Raman spectroscopies. The current–voltage (dc I– V) characteristics as well as the results of time response measurements are also presented.