Double-barrier Quantum Wells Research Articles

Electronic and transport properties of U-cut edge patterned AGNR superlattice for RTD application

In this paper, we first characterize a superlattice structure created by repeating a heterostructure formed from two armchair graphene nanoribbon (AGNR) segments with different widths. We investigate the electronic and transport properties of this structure by varying its widths and lengths to demonstrate the tunability of its overall band gap. The plot of the local density of states shows the formation of localized states at the low band gap segments of the superlattice. The superlattice is then used as a barrier to create a double barrier quantum well (DBQW) to design a proposed resonant tunneling diode (RTD) structure. We observe this device's negative differential resistance (NDR) operation for a range of bias voltages between the contacts. We study the effect of dimensional parameters on the RTD performance. The non-equilibrium Green's function method, based on a tight-binding model, is employed for numerical computation.

Development of a simple two-step lithography fabrication process for resonant tunneling diode using air-bridge technology

This article reports on the development of a simple two-step lithography process for double barrier quantum well (DBQW) InGaAs/AlAs resonant tunneling diode (RTD) on a semi-insulating indium phosphide (InP) substrate using an air-bridge technology. This approach minimizes processing steps, and therefore the processing time as well as the required resources. It is particularly suited for material qualification of new epitaxial layer designs. A DC performance comparison between the proposed process and the conventional process shows approximately the same results. We expect that this novel technique will aid in the recent and continuing rapid advances in RTD technology.

Room-temperature electroluminescence and light detection from III-V unipolar microLEDs without p-type doping

The twentieth-century semiconductor revolution began with “man-made crystals,” or p-n junction-based heterostructures. This was the most significant step in the creation of light-emitting diodes (LEDs), lasers, and photodetectors. Nonetheless, advances where resistive p-type doping is completely avoided could pave the way for a new class of n-type optoelectronic emitters and detectors to mitigate the increase of contact resistance and optical losses in submicrometer devices, e.g., nanoLEDs and nanolasers. Here, we show that nanometric layers of AlAs/GaAs/AlAs forming a double-barrier quantum well (DBQW) arranged in an n-type unipolar micropillar LED can provide electroluminescence (EL) (emission at 806 nm from the active DBQW), photoresponse (responsivity of 0.56 A/W at 830 nm), and negative differential conductance (NDC) in a single device. Under the same forward bias, we show that enough holes are created in the DBQW to allow for radiative recombination without the need of p-type semiconductor-doped layers, as well as pronounced photocurrent generation due to the built-in electric field across the DBQW that separates the photogenerated charge carriers. Time-resolved EL reveals decay lifetimes of 4.9 ns, whereas photoresponse fall times of 250 ns are measured in the light-detecting process. The seamless integration of these multi-functions (EL, photoresponse, and NDC) in a single microdevice paves the way for compact, on-chip light-emitting and receiving circuits needed for imaging, sensing, signal processing, data communication, and neuromorphic computing applications.

Surface passivation in c-Si solar cells via a double-barrier quantum-well structure for ameliorated performance

Modern solar cell technology suffers low surface passivation, high recombination losses at the interface, and dopant diffusion losses that limit solar cell’s efficiency. Therefore, a double-barrier quantum-well (DBQW) structure-based surface passivation contact is introduced here to resolve these shortcomings. In this regard, DBQWs of different thicknesses with stacks of SiOx/ nc-SiOx (3, 5, 8, and 10 nm)/SiOx layers were explored as surface passivation layers and dopant diffusion barriers. Multiple characterizations were utilized to examine DBQW thickness-dependent properties, such as contact resistance, passivation, and recombination current density; the best result was for the 5-nm-thickness QW passivation layer. To justify the obtained result, theoretical calculations were carried out based on the experimental results, which suggested the resonance tunneling of charge carriers across the 5 nm DBQW structure. Furthermore, SIMS was explored to examine the diffusion barrier property of these QWs, which revealed that dopant diffusion was suppressed by the QW with the double SiOx layer. Finally, the nc-SiOx(n) /5-nm QW/c-Si surface passivation structure showed substantial enhancement in a lifetime (τeff) of 3560 μs, an implied open-circuit voltage (iVoc) of 735 mV, and reduced recombination current density (Jo) = 1.5 fA/cm2.

P‐Type Doped AlAsSb/GaSb Resonant Tunneling Diode Photodetector for the Mid‐Infrared Spectral Region

AbstractMid‐infrared (MIR) resonant tunneling diode (RTD) photodetectors based on a p‐type doped AlAsSb/GaSb double‐barrier quantum well (DBQW) are proposed and investigated for their optoelectronic transport properties. At room temperature, a distinct resonant tunneling current with a region of negative differential conductance is measured. The peak‐to‐valley current ratio (PVCR) is 1.51. To provide photosensitivity within the MIR spectral region, a lattice‐matched quaternary low‐bandgap GaInAsSb absorption layer with cutoff wavelength of λ = 2.77 μm is integrated near the DBQW. Under illumination with infrared light, photogenerated minority electrons within the absorption layer can drift toward the DBQW, where they accumulate and cause a shift of the current–voltage characteristics toward smaller bias voltages, which can be exploited to measure the incident MIR light power. In a tunable diode laser absorption spectroscopy experiment, the RTD photodetector is used to identify three distinct water absorption lines in the MIR close to λ = 2.61 μm. By adjusting the absorption layer doping concentration, the RTD quantum efficiency can be increased by a factor of 10, resulting in a sensitivity of S = 2.71 A W−1, which corresponds to an estimated multiplication factor of M = 8.6.

Modeling of tunneling current density of GeC based double barrier multiple quantum well resonant tunneling diode

The double barrier quantum well (DBQW) resonant tunneling diode (RTD) structure made of SiGeSn/GeC/SiGeSn alloys grown on Ge substrate is analyzed. The tensile strained Ge1−zCz on Si1−x−yGexSny heterostructure provides a direct band gap type I configuration. The transmission coefficient and tunneling current density have been calculated considering single and multiple quantum wells. A comparative study of tunnelling current of the proposed structure is done with the existing RTD structure based on GeSn/SiGeSn DBH. A higher value of the current density for the proposed structure has been obtained.

Effects of self-affine roughness characteristics on electron transmission through tunneling structures

By using the transfer matrix method and the nearly free electron approximation, we investigate effects of interfacial roughness on electron transport through double-barrier quantum wells. The barrier roughness is described by the k-correlation model, and the interface is characterized by the roughness exponent, in-plane correlation length, and root mean square height. Our analysis demonstrates that the transmission probability is sensitive to roughness parameters. Two behaviors are observed for this sensitivity depending on whether the incident wavelength is larger or smaller than the correlation length.

Light propagation characteristics of one-dimensional photonic crystal with double-barrier quantum well

The light transfer characteristics of one-dimensional photonic crystal with single and double-barrier quantum well are studied by transfer matrix method. The results show that when the refractive index of the barrier layer is high, the transmission peaks in single-barrier quantum well of photonic crystal will be narrower and the inner localized field will be stronger, that the peak in the double-barrier is narrower than the one in the single-barrier, and also the inner localized field is stronger in the double-barrier, that with the number of period layer in the photonic crystal increasing, the inner localized field in the double-barrier well is enhanced, furthermore, the bigger the refractive index ratio between barrier and dielectric layers of well, the stronger the inner localized field in the photonic crystal quantum well is. In addition, when the periodicity of the barrier layer in the photonic crystal with a thicker refractive index increases, the inner localized field will strengthen faster, and accordingly, the transmittance of the transmission peak will decrease more quickly. Both of the strengthening and decreasing will work at the top speed when all periods in different barriers increase at the same time. While the period number of the photonic crystal in well layers increases, the inner localized fields in both single and double-barrier will increase, but their transmittances of the transmission peak will keep the same. The characteristics above can provide guidance for designing new high-quality quantum optical devices.

Detemining the Thickness of Barriers and Well of Resonance Tunneling Diodes by Specified I-V Characteristic

In this paper, a method of determining physical dimension of Double Barrier Quantum Well (DBQW) of Resonance Tunneling Diodes (RTDs) is presented by using I-V characteristic governing on them. In this procedure, first we have used performance metrics related to RTDs I-V characteristic such as Peak to Valley Current Ratio (PVCR), peak current density (JP), valley current density (JV) and Voltage Swing (VS), and by some other arbitrary points, we have fitted a curve to the RTD current-voltage equation by MATLAB software. Then we have obtained the physical parameter of I-V equation and adjusted some of them with modification coefficients. Next, by choosing the material of barriers and the well and amount of doping, we have calculated the thicknesses of both. To review the mentioned method, the experimental result of I-V characteristic of the sample structure DBQW is considered and we have come to this idea that the dimensions gained out of this method are highly correlated with those of the experimental sample.

Spin-dependent tunneling through double-barrier quantum wells with random corrugation interfacial roughness

We use the transfer matrix method to study spin-dependent tunneling transmission through the NM/EuS/NM/EuS/NM junction which affected by random corrugation interfacial roughness. The temperature dependence of spin-splitting energy is calculated for EuS magnetic barrier within the mean-field approximation. We perform several calculations to study the effect of random nonplanar interfacial on transmission probability for several widths of quantum well at different temperatures. Our results show that the scattering process due to random roughness open the new conduction channels (the dip and peak resonance energies). The results may be useful in designing spintronic devices.

Shape effects in graphene nanoribbon resonant tunneling diodes: A computational study

The possibility of using graphene nanoribbons (GNRs) as the material for resonant tunneling diodes (RTDs) was investigated using a device simulator based on the nonequilibrium Green’s function with the π-orbital tight-binding approach. The double-barrier quantum well (DBQW) requirements of a RTD can be implemented by adjusting the width of a GNR to derive a negative differential resistance (NDR). The implementation of such a device is demonstrated in this paper and its mechanism was also found to be robust regardless of the eventual shape of the GNR patterned. Furthermore, the effects of the shape of the patterned GNR and the operating temperature on the performance of the device were explored by looking at the real space current flux of the device and the temperature dependency of the peak-valley ratio (PVR), respectively. Although the different shapes of GNR RTDs had a similar DBQW structure, their PVRs were different due to their conduction mechanisms which were dependent on the different geometrical shapes of each case. Lastly, the effect of thermal broadening, and width/length dependence of the central GNR between two barriers on the device performance, was further investigated in order to provide insights into the device physics of GNR RTDs for future study on performance optimization.

Dilute nitride based double-barrier quantum wells for intersubband absorption at 1.31 and1.55 μm

A systematic investigation of intersubband optical absorptions in ${\text{In}}_{x}{\text{Ga}}_{1\ensuremath{-}x}{\text{As}}_{1\ensuremath{-}y}{\text{N}}_{y}/\text{AlAs}/{\text{Al}}_{z}{\text{Ga}}_{1\ensuremath{-}z}\text{As}$ double-barrier quantum well (DBQW) structures is reported. Electron subbands and the energy dependent effective potential for the envelope wave functions are calculated by means of the ten-band $k\ensuremath{\cdot}p$ scheme, which takes into account the effects of subband nonparabolicity and strain. From the calculations of the energy dispersions and wave functions of the respective states, we find that when the conduction-band offset is very large such that the first excited state lies above the localized nitrogen level, each of the ground and the first excited states is split into two levels. The intersubband absorptions in the DBQW structure have been studied by varying the well width and the compositions of the alloys. The strongest calculated absorption peak corresponding to the transition from the ground level to the higher excited level shows the same peculiarities. Finally, DBQW structures, which correspond to 1.31 and $1.55\text{ }\ensuremath{\mu}\text{m}$ intersubband absorptions, respectively, have been achieved.

Offset in the dark current characteristics of photovoltaic double barrier quantum well infrared photodetectors

The double barrier quantum well (DBQW) structure based on AlGaAs/AlAs/GaAs represents a promising design for infrared detectors operating in the 3–5 μm range. Nevertheless, this structure is affected by some unexpected and intriguing features which must be taken into account for its practical operation, i.e. the remarkable photovoltaic (PV) effect observed in detectors doped in the QW and the appearance of anomalies in the dark current ( I d) characteristics at T < 60 K. In this work, we focus on the study of the anomalies in I d, in particular the presence of a non-zero current (offset) at zero bias. We report that the offsets are time independent, with negligible hysteresis effects. Additionally we find a closely link between the offsets and the unintentional PV response. Although so far we do not have any clear explanation for the offset, we have found that its appearance may relate to a change in the preferential escape direction of electrons in the dark, which is related to a change from tunnelling-assisted thermionic emission to tunnelling emission. This interpretation is based on the experimental result that the temperature at which the offset first appears agrees with the transition temperature in the mechanisms controlling I d and with the temperature where a reversal in the electron flux direction is found. These results are reproducibly found in all the DBQW samples we have studied.

Intersubband absorption from 2 to 7 µm in strain-compensated double-barrier InxGa1−xAs multiquantum wells

We report observations of strong room temperature intersubband absorption in strain-compensated In0.84Ga0.16As/AlAs/In0.52Al0.48As double-barrier quantum wells grown on InP substrates. Multiple Γ → Γ intersubband transitions have been observed across a wide range of the mid infrared spectrum (2–7 µm) in three structures of differing InGaAs well width (30 Å, 45 Å and 80 Å) and therefore with differing net strain. This absorption range is not covered by direct-gap GaAs/AlGaAs structures.

Comment on “Effects of the localized state inside the barrier on resonant tunneling in double-barrier quantum wells”

Comment on “Effects of the localized state inside the barrier on resonant tunneling in double-barrier quantum wells”

Subband nonparabolicity estimated from multiple intersubband absorption in highly doped multiple quantum wells

We report strong room-temperature intersubband absorption in 80 \AA{} strain-compensated ${\mathrm{In}}_{0.84}{\mathrm{Ga}}_{0.16}{\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{A}\mathrm{s}/\mathrm{I}\mathrm{n}}_{0.52}{\mathrm{Al}}_{0.48}\mathrm{As}$ double-barrier quantum wells grown on InP substrates. From the multiple \ensuremath{\Gamma}-\ensuremath{\Gamma} intersubband transitions observed, it is inferred that the electron effective masses and nonparabolicity parameters for the first two subbands differ significantly from each other. For the range $k\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{6}--6\ifmmode\times\else\texttimes\fi{}{10}^{6}{\mathrm{cm}}^{\ensuremath{-}1},$ the difference in subband parameters results in a change in transition energy of about twice the value calculated for the corresponding GaAs/AlGaAs quantum well.

Highly strained [formula omitted] layers for short wavelength QWIP and QCL structures grown by MBE

Highly strained quantum cascade laser (QCL) and quantum well infrared photodetector (QWIPs) structures based on In x Ga (1−x) As−In y Al (1−y) As (x>0.8,y<0.3) layers have been grown by molecular beam epitaxy. Conditions of exact stoichiometric growth were used at a temperature of ∼420°C to produce structures that are suitable for both emission and detection in the 2– 5 μm mid-infrared regime. High structural integrity, as assessed by double crystal X-ray diffraction, room temperature photoluminescence and electrical characteristics were observed. Strong room temperature intersubband absorption in highly tensile strained and strain-compensated In 0.84Ga 0.16As/AlAs/In 0.52Al 0.48As double barrier quantum wells grown on InP substrates is demonstrated. Γ– Γ intersubband transitions have been observed across a wide range of the mid-infrared spectrum (2– 7 μm ) in three structures of differing In 0.84Ga 0.16As well width (30, 45, and 80 A ̊ ). We demonstrate short-wavelength IR, intersubband operation in both detection and emission for application in QC and QWIP structures. By pushing the InGaAs–InAlAs system to its ultimate limit, we have obtained the highest band offsets that are theoretically possible in this system both for the Γ– Γ bands and the Γ–X bands, thereby opening up the way for both high power and high efficiency coupled with short-wavelength operation at room temperature. The versatility of this material system and technique in covering a wide range of the infrared spectrum is thus demonstrated.

GaAsN/AlAs/AlGaAs double barrier quantum wells grown by molecular beam epitaxy as an alternative to infrared absorption below 4 μm

In this work, we report on the design, growth and characterization of GaAsN/AlAs/AlGaAs double barrier quantum well infrared detectors to achieve intraband absorption below 4 μm. Due to the high effective mass of N-dilute alloys, it is common for these N-containing double barrier quantum well structures to have more than one bound state within the quantum well, enabling the possibility of achieving multispectral absorption from these confined levels to the quasi-bound. Based on a transfer matrix calculation we will study the influence of the potential parameters, in particular the well width and the introduction of a GaAs spacer layer in between the N-well and the AlAs barriers. We will compare the case in which there are two confined levels with the case in which only one level is bound, like in the conventional AlGaAs/AlAs/GaAs structures. On the basis of the simulation, we have grown and characterized some N-containing double barrier detectors. Moreover, an optimization of the post-growth annealing treatments of the GaAsN quantum well structures has also been performed. Finally, room temperature absorption measurements of both as-grown and annealed samples are presented and analyzed.

Observation of intersubband absorption in the forbidden polarisation for a stepped double barrier quantum well

Intersubband absorption in the conduction band of a series of double barrier multiple quantum wells has been studied. Absorption in the forbidden polarisation was observed for a GaAs/Inx Ga(1-x) As/AlAs/Aly Ga(1 - y) As stepped well using 45° waveguide geometry. This is attributed to the relaxation of the polarisation selection rule. This corroborates the authors' previous observation of enhanced absorption at the Brewster angle in these structures. In 45° waveguide geometry, it is possible to resolve Γ(well)–X(AlAs) transitions in some samples. The observed energies of both Γ–Γand Γ–X transitions are in good agreement with the proposed theoretical model using an X-band effective mass of 0.4mo.

Characteristics of electron transport through vertical double-barrier quantum-dot structures: Effects of symmetric and asymmetric variations of the lateral confinement potentials

We report on a theoretical study of the electron transport through laterally-confined, vertical double-barrier resonant-tunneling (DBRT) structures, defined as one-dimensional (1D)-0D-1D systems, with a tunable lateral confinement. The current and the differential conductance of the systems are calculated and the influence caused by varying the lateral confinement on the device characteristics is investigated. Three representative systems are studied. First of all, a 1D-0D-1D device, symmetric with respect to the current flow, with a variable lateral confinement in the double-barrier quantum-well (DBQW) region, is investigated. This device would in an experimental setup correspond to the structure in which a thin, lateral metallic gate is placed in the DBQW region. Subsequently, calculations are performed for two asymmetric 1D-0D-1D devices, in which the strongest, but varying, lateral confinement is placed either in the collector or in the emitter region. In experiments, these two devices would correspond to the situations where a lateral metallic gate is positioned below or on top of the DBQW structure. The calculations predict several phenomena for the device characteristics. It is shown that as the lateral confinement increases, in addition to those normally observed current onsets and pinch-offs that move toward higher bias voltages, several current onsets and pinch-offs move towards lower bias voltages. These negative shifts of the current onsets and pinch-offs with increasing of the lateral confinement have so far not been expected for gated DBRT devices. It is also found that the threshold voltages, at which the current onsets and pinch-offs appear, depend strongly on the strength and position of the lateral confinement and on the Fermi levels in the collector and the emitter. The models that explain these predictions are presented and discussed.