Superlattice Barriers Research Articles

Fabrication and formation mechanisms of ohmic conducts with low annealing temperature for GaN/AlN superlattice barrier HEMTs

Fabrication and formation mechanisms of ohmic conducts with low annealing temperature for GaN/AlN superlattice barrier HEMTs

Magnetic tunnel junctions with superlattice barriers

The urgent demand for high-performance emerging memory, propelled by artificial intelligence in internet of things (AIoT) and machine learning advancements, spotlights spin-transfer torque magnetic random-access memory as a prime candidate for practical application. However, magnetic tunnel junctions (MTJs) with a single-crystalline MgO barrier, which are central to magnetic random-access memory (MRAM), suffer from significant drawbacks: insufficient endurance due to breakdown and high writing power requirements. A superlattice barrier-based MTJ (SL-MTJ) is proposed to overcome the limitation. We first fabricated the MTJ using an SL barrier while examining the magnetoresistance and resistance-area product. Lower writing power can be achieved in SL-MTJs compared to MgO-MTJs. Our study may provide a new route to the development of MRAM technologies.

Spin-dependent shot noise in 8-Pmmn borophene based-superlattice

The effect of the Rashba spin-orbit interaction on the shot noise, spin/valley polarization in 8-Pmmn borophene-based superlattice are studied theoretically, by applying the transfer-matrix approach. The spin-dependent transmission probability can be easily controlled by the number of superlattice barriers, the strength of the Rashba, and the incident electron angle. The Fano factor without spin rotation as well as with spin rotation shows an oscillatory pattern versus the strength of the Rashba, and the oscillatory behavior becomes more pronounced as the number of barriers increases. Also, the Fano factor shows a strong dependence on the superlattice direction and number of barriers. The spin and valley polarizations can be easily controlled by the number of barriers and the direction of superlattice. Our findings in this work could provide useful for valleytronics/spintronics systems based on the 8-Pmmn borophene.

Superhigh gain InGaN/GaN visible-light photodetector using polarization heterointerface barrier and single-carrier superlattices

Visible-light detection with high sensitivity and strong wavelength selectivity is highly desired in emerging applications. Here, we demonstrate a high-performance visible-light photodetector with an active region composed of a polarization induced barrier and single-carrier superlattices (SCSLs). The barrier at SCSLs/GaN heterointerface brings both a low dark current and a high gain originating from the photoinduced barrier reduction effect. Meanwhile, the designed InGaN/GaN SCSLs allow the photoelectrons in the quantum wells to escape, but photogenerated holes are weakly localized, thus generating the additional photoconductive gain. The resulting devices exhibited a super-high gain of 7.8 × 104, a large detectivity of 1.2 × 1016 jones, and a relatively fast response speed with rise/falling time of 2.5/89.6 ns. Also, a 400/500-nm rejection ratio greater than 3 × 105 was shown at 1 V, indicating excellent wavelength selectivity.

Effect of Asymmetric InAlGaN/GaN Superlattice Barrier Structure on the Optoelectronic Performance of GaN-Based Green Laser Diode

An asymmetric InAlGaN/GaN superlattice barrier structure without the first quantum barrier layer (FQB) is designed, and its effect on the optoelectronic performance of GaN-based green laser diode (LD) has been investigated based on simulation experiment and analytical results. It is found that, compared with conventional GaN barrier LD, device performance is significantly improved by using FQB-free asymmetric InAlGaN/GaN superlattice barrier structure, including low threshold current, high output power, and high photoelectric conversion efficiency. The threshold current of LD with novel structure is 16.19 mA, which is 22.46% less than GaN barrier LD. Meanwhile, the output power is 110.69 mW at an injection current of 120 mA, which is 16.20% higher compared to conventional LD, and the wall-plug efficiency has an enhancement of 9.5%, reaching 20.27%. FQB-free asymmetric InAlGaN/GaN superlattice barrier layer can reduce optical loss, suppress the polarization effect, and improve the carrier injection efficiency, which is beneficial to improve output power and photoelectric conversion efficiency. The novel epitaxial structure provides theoretical guidance and data support for improving the optoelectronic performance of GaN-based green LD.

Effect of the magnetic field on the conductance and spin polarization in phosphorene superlattice

The spin-dependent conductance and spin polarization are investigated theoretically in a phosphorene superlattice in the presence of external magnetic field and Rashba interaction. It is demonstrate that, the spin-dependent conductance with and without spin-flip as well as spin polarization can be effectively controlled by changing the magnetic field strength and the number of the superlattice barriers. For small magnetic field strength, the conductance for with and without spin-flip shows an oscillating behavior as increasing the strength of the Rashba interaction, and by increasing the number of barriers, the oscillating behavior becomes prominent. Further, when the magnetic field is greater than a limit value, the spin conductance will be zero. The size of the spin-dependent transmission window in the phosphorene superlattice under external magnetic field decreases drastically. The magnitude, sign and behavior of the spin polarization can be tuned by the amount of the external magnetic field.

Effect of “M” and “B” superlattice barrier layers on dark current of long-wavelength infrared detectors

This paper studies superlattice materials with M barrier (InAs/GaSb/AlSb/GaSb superlattice) and B barrier (InAs/AlSb superlattice) structures. Firstly, it introduces the diffusion current, generation-recombination current, tunneling current and surface leakage current in devices, and analyzes the factors affecting different dark current mechanisms. Secondly, it theoretically analyzes the influence of the two barrier structures on device performance. Finally, devices were fabricated using these two structures, and the device performance was characterized. At a bias voltage of −50 mV and operating temperature of 77K. The PπMN type long-wave infrared (LWIR) detector has an RA of 91.4 Ω cm2 and a LW dark current density of 3.51 × 10−4 A cm−2. The PπBN type LWIR detector has an RA of 439 Ω cm2 and a LW dark current density of 2.81 × 10−4 A cm−2. Meanwhile, by fitting the data at different temperatures, the activation energy Ea of the PπMN type LWIR detector is 119.8 meV, with dark current mainly determined by diffusion current and generation-recombination current. The activation energy Ea of the PπBN type LWIR detector is 126.2 meV, with dark current mainly determined by diffusion current. This experimentally verifies the dominant dark current mechanisms for the two barrier structures of LWIR detectors, providing strong support for the design of superlattice detector structures.

Performance analysis of an InAs/GaSb superlattice barrier photodetector covering the full LWIR spectral domain

Performance analysis of an InAs/GaSb superlattice barrier photodetector covering the full LWIR spectral domain

Electro-optical performance and anisotropic transport study of a Ga-free type-II superlattice barrier structure

Electro-optical performance and anisotropic transport study of a Ga-free type-II superlattice barrier structure

Mid-wavelength InAs/GaSb type-II superlattice barrier detector with nBn design and M barrier

Mid-wavelength InAs/GaSb type-II superlattice barrier detector with nBn design and M barrier

Effect of the Rashba interaction on the tunneling time and Hartman effect in an 8-Pmmn borophene superlattice

The spin-dependent group delay time and Hartman effect as well as the valley/spin polarization in an 8-Pmmn borophene superlattice under Rashba interaction are investigated theoretically, by using the stationary phase and the transfer matrix approaches. The group delay time depends on the spin degree of freedoms, and can be effectively controlled by changing the direction of superlattice, incident electron angle and Rashba strength. Both the valley and spin polarization reveal a strong dependence on the number of the superlattice barriers. Furthermore, group delay time oscillates as the width of the potential barriers increases, but in special conditions, the dependence on the width of the potential barriers will disappear. Interestingly, by increasing the angle of the direction of the superlattice the Hartman effect can be observed for most electron incidence angles. Our study show that, the 8-Pmmn borophene superlattice can be useful for future electronics and spintronics applications.

Electric-field driven source of photocarriers for tunable electron spin polarization in InGaAs quantum dots

Electric-field control of spin polarization of electrons during injection into InGaAs quantum dots (QDs) was studied via circularly polarized time-resolved photoluminescence. Electric-field modulation of optical spin polarization in QDs will play a key role in future progress of semiconductor opto-spintronics. The tuning of band potentials by applying external electric fields can not only affect spin-injection efficiencies but also switch dominant spin-injection layers. In this study, we developed a QD-based electric-field-effect optical spin device with two different spin-injection layers, which consisted of a GaAs and GaAs/Al0.15Ga0.85As superlattice (SL) barriers. The bias-voltage modulation of the optical spin polarization in QDs was demonstrated by changing the spin polarization degree of electrons injected from these barriers into the QD via the electric-field switching of the spin-injection layers. This was achieved by exploiting the difference in spin relaxation properties between bulk GaAs and the SL. This proposed structure, which comprised of one luminescent layer and two spin-injection layers, is highly scalable because the modulation range of optical spin polarization can be enhanced by changing the combination of spin-injection layers, as well as the material used and its layer thickness.

Spin-dependent tunnelling time in phosphorene superlattice

ABSTRACT We study theoretically the Hartman effect and spin-dependent group delay time in a strained phosphorene superlattice in the presence of Rashba spin–orbit interaction (RSOI). It is found that the total group delay time depends on the spin degree of freedom. Thus, spin filtering can be obtained in the time domain by means of the phosphorene superlattice. The total group delay time can be efficiently controlled by the angles of incidence of electrons, strength of RSOI and number of superlattice barriers. Particularly, the magnitude of the total group delay time can be tuned via the direction and strength of strain. Therefore, in phosphorene superlattice the total group delay time can be efficiently adjusted mechanically. Moreover, in a strained phosphorene superlattice the superluminal tunnelling or Hartman effect can be observed even for a normal incident.

Impact of illumination on quantum lifetime in selectively doped GaAs single quantum wells with short-period AlAs/GaAs superlattice barriers

Impact of illumination on high-mobility dense 2D electron gas in selectively doped single GaAs quantum well with short-period AlAs/GaAs superlattice barriers at T=4.2 K in magnetic fields B<2 T has been studied. It was demonstrated that illumination at low temperatures gives rise to enhancement of electron density, mobility and quantum lifetime in studied heterostructures. The enhancement of quantum lifetime after illumination for single GaAs quantum well with modulated superlattice doping had been explained as consequence of decrease in effective concentration of remote ionized donors. Keywords: persistent photoconductivity, quantum lifetime, anisotropic mobility, superlattice barriers.

Shubnikov-de Haas oscillations in 2D electron gas with anisotropic mobility

Shubnikov-de Haas oscillations in selectively doped GaAs single quantum wells with AlAs/GaAs superlattice barriers has been studied at temperature T=4.2 K in magnetic fields B<1 T. High-mobility heterostructures with thin spacer had been grown by molecular-beam epitaxy on (001) GaAs substrates. The mobilities of two-dimensional electron gas measured in two crystallographic directions [110] and [110] differ from each other more than 50%. Properly adapted expression for Shubnikov-de Haas oscillations amplitudes in anisotropic samples has been used for correct analysis of this oscillations. It was stated that quantum life-time in our heterostructures as measured by Shubnikov-de Haas oscillations on Hall bars oriented in the directions [110] and [110] varies less than 5%. Obtained results show that quantum life-time in two-dimensional electron system with anisotropic mobility is isotropic with aforementioned accuracy. Keywords: Shubnikov-de Haas oscillations, anisotropic mobility, quantum life-time, superlattice barriers.

Осцилляции Шубникова-де Гааза в двумерном электронном газе с анизотропной подвижностью

Abstract Shubnikov de Haas oscillations in selectively doped GaAs single quantum wells with AlAs/GaAs superlattice barriers has been studied at temperature T = 4.2 K in magnetic fields B < 1 Т. High-mobility heterostructures with thin spacer had been grown by molecular-beam epitaxy on (001) GaAs substrates. The mobilities of two-dimensional electron gas measured in two crystallographic directions [110] and [-110] differ from each other more than 50%. Properly adapted expression for Shubnikov de Haas oscillations amplitudes in anisotropic samples has been used for correct analysis of this oscillations. It was stated that quantum life-time in our heterostructures as measured by Shubnikov de Haas oscillations on Hall bars oriented in the directions [110] and [-110] varies less than 5%. Obtained results show that quantum life-time in two-dimensional electron system with anisotropic mobility is isotropic with aforementioned accuracy.

Novel E-mode GaN high-electron-mobility field-effect transistor with a superlattice barrier doped with Mg by thermal diffusion

A novel E-mode GaN high-electron-mobility field-effect transistor with a superlattice barrier doped with Mg by thermal diffusion. This strategy can provide new ideas for the commercialisation of E-mode devices.

Determination of the electron distribution in thin barrier AlGaAs/GaAs superlattices by capacitance-voltage profiling

Electron density distribution in uniformly doped AlGaAs/GaAs superlattices with respective layer thicknesses 1.5/10 nm and a different number of quantum wells was investigated. Experimental samples containing 3, 5 and 25 periods with the same layer parameters were grown by molecular beam epitaxy. Capacitance-voltage profiling was used to determine the carrier concentration profiles in the structures both numerically and experimentally. During the analysis of experimental capacitance-voltage characteristics it was found that the maximum electron concentration increases with an increase in the number of quantum wells starting from 7,1∙1016 сm–3 for 3 wells up to 9,2∙1016 сm–3 for 25 wells with overall superlattice doping level of 1017 сm–3. In some samples saturation areas are observed on the concentration profiles, that are associated with the region of superlattice. Concentration values, obtained from computer modeling, correspond to the experimental data with an error of less than 10 %. Capacitance-voltage profiling is a suitable technique for determining the carrier concentration profiles in thin barrier superlattices. Despite the fact that the method provides distribution of the “apparent” carrier concentration profile, it can be used to estimate the dopant atoms distribution in the strongly coupled quantum well heterostructures.

Temperature Dependence Study of Electrical and Electro-Optical Performances of Midwave Infrared Ga-Free T2SL Barrier Photodetector

In this paper, we report on temperature dependence performances of a midwave infrared (MWIR) Ga-free InAs/InAsSb type-II superlattice (T2SL) barrier (XBn) photodetector grown by molecular beam epitaxy on n-type GaSb substrate. The T2SL structure, with a 3 µm thick active region, was processed in a mesa device in order to perform dark current measurements and spectral photoresponse as a function of temperature. Analyses of these temperature dependence characterizations help us to improve the design of Ga-free T2SL MWIR XBn detectors.

Spin dependent Goos–Hänchen-like effect in a strained phosphorene superlattice

Herein, we present a theoretical study on the Goos–Hänchen (GH)-like effect in a phosphorene superlattice in the presence of strain and an external Rashba spin-orbit interaction (ERSOI). The spin-up and spin-down electrons have different GH shifts and their separation can be tuned via the angle of incidence of the electrons, ERSOI strength, direction strain and strength of strain. The results show that the GH shift exhibits an oscillatory evolution with the ERSOI strength, barrier width, and strain strength. In addition, the GH shift can have negative as well as positive values, and the magnitude of the spin-dependent GH shift can be efficiently controlled by the number of superlattice barriers and mechanically. Interestingly, in a strained phosphorene superlattice under special conditions, the GH shift of the electrons with and without spin-flipping increases linearly by the barrier width, which can be related to the Hartman effect.