High speed switching and power dissipation in heterojunction double barrier diodes

A theoretical analysis of the dynamical aspects of high speed switching between different stable states in bistable circuits containing quantum well devices with negative differential resistance is presented. A variational calculus method is introduced to obtain the minimal energy dissipation required for a given switching time. Results are presented for individual heterojunction double barrier diode and for pairs of heterojunction double barrier diodes which are connected in series.     

Physical basis for the negative resistance in double heterostructure injection lasers

The previously observed negative resistance in double heterostructure diodes is shown to be caused by a trap generated potential barrier near the heterojunctionnGa_1-x Al _x As−pGaAs. The filling and emplying times were measured by observing the breakdown of the barrier with single and double pulses. Time resolved spectral measurements confirm the model.     

Microwave impedance measurements on resonant tunnelin diodes with asymmetric spacer layers

Scattering parameters (S parameters) have been measured up to 40GHz on GaAs/AlAs resonant tunneling diodes containing asymmetric spacer layers. On-wafer microwave probing techniques were used. A hysteresis was observed in the vicinity of the negative differential resistance (NDR) region. Unlike the one observed in dc current-voltage measurements, this hysteresis was not affected by oscillations and believed to be intrinsic. The impedance data has been fitted to a lumped equivalent circuit model and capacitance-voltage (C-V) characteristic extracted. In addition to the already reported capacitance peak in the NDR region, a smaller peak at a lower voltage was found. In comparison to the self-consistent calculation, the smaller peak is due to the electrons discharging from accumulation region between the emitter barrier and the cathode spacer layer. The C-V result agrees qualitatively with the theoretical calculation. It supports the theoretical argument that the negative conductance can be increased by increasing the cathode spacer layer, however, there is also an increase in capacitance and the cutoff frequency may be reduced.     

Dependence of current-voltage characteristics of pseudomorphic AlAs/In0.53a0.47s/InAs resonant tunneling diodes on quantum well widths

This paper studies the dependence of I-V characteristics on quantum well widths in AlAs/In_0.53Ga_0.47As and AlAs/In_0.53Ga_0.47As/InAs resonant tunneling structures grown on InP substrates. It shows that the peak and the valley current density in the negative differential resistance region are closely related with quantum well width. The measured peak current density, valley current densities and peak-to-valley current ratio of resonant tunneling diodes are continually decreasing with increasing well width.     

Discrete electroluminescence lines in sub-micron p-i-n resonant tunnelling diodes

We have fabricated GaAs/AlAs p-i-n double barrier resonant tunnelling diodes with active lateral dimensions down to 0.25μn² using optical lithography and wet etching. Many devices have been investigated and systematic variations in the quantum well emission have been observed as the device size is decreased. We observe a red shift of the quantum well recombination lines. In addition a new line is observed at lower energy in the spectra of the smallest devices. The quantum well luminescence efficiency is found to be constant down to the smallest device size.     

Nonlinear transport in p-type SiGe quantum well structure containing Ge quantum dots

We use magneto-transport spectroscopy to study a dramatic instability between a low and high conductivity mode in Si/SiGe-based resonant tunneling diodes with an embedded layer of self-assembled Ge hut cluster quantum dots in the Si barrier. In the low current regime a simple activation-type behavior with an astonishingly low activation energy in the order of 0.1 meV is determined. In the high current regime a region of negative differential conduction can be observed. We discuss the influence of different layer structures and magnetic fields.     

Magneto-tunneling spectroscopy of GaAs---AlGaAs double barrier tunneling devices in pulsed high magnetic fields up to 40T

The magneto-tunneling effect was investigated in GaAs---AlGaAs double barrier resonant tunneling devices in pulsed high magnetic fiels up to 40T applied parallel(B) and perpendicular (B) to the barrier layers. In a sample with , oscillatory structures due to the 2D electrons in the emitter and the LO phonon assisted resonant tunneling were observed when the magnetic field (B) was swept at constant bias voltages. A large drop of the current was found in the quantum limit at applied voltages below the negative differential conductivity region. A striking hysteresis was observed in the voltage-current (V - I) curves. In a wide well sample with , rich structures were observed in the V - I curve for B, corresponding to the tunneling to different cyclotron orbits from the emitter.     

Piezoelectric polarization and quantum size effects on the vertical transport in AlGaN/GaN resonant tunneling diodes

In this work,the electronic properties of resonant tunneling diodes(RTDs) based on GaN-AlxGa(1-x)N double barriers are investigated by using the non-equilibrium Green functions formalism(NEG).These materials each present a wide conduction band discontinuity and a strong internal piezoelectric field,which greatly affect the electronic transport properties.The electronic density,the transmission coefficient,and the current–voltage characteristics are computed with considering the spontaneous and piezoelectric polarizations.The influence of the quantum size on the transmission coefficient is analyzed by varying GaN quantum well thickness,Al_xGa_(1-x)N width,and the aluminum concentration x_(Al).The results show that the transmission coefficient more strongly depends on the thickness of the quantum well than the barrier;it exhibits a series of resonant peaks and valleys as the quantum well width increases.In addition,it is found that the negative differential resistance(NDR) in the current–voltage(I–V) characteristic strongly depends on aluminum concentration xAl.It is shown that the peak-to-valley ratio(PVR) increases with xAlvalue decreasing.These findings open the door for developing vertical transport nitrides-based ISB devices such as THz lasers and detectors.     

Computer simulation of the small-signal admittance and negative resistance of double avalanche region IMPATT diodes

A generalized small-signal computer simulation of double avalanche region (DAR) n ⁺-p-v-n-p ⁺ Si and InP IMPATT diodes has been carried out for different frequencies and current densities taking both drift and diffusion of charge carriers into account. The simulation results show that both symmetrically and asymmetrically doped devices based on Si and InP exhibit discrete negative conductance frequency bands separated by positive conductance frequency bands. The magnitudes of both negative conductance and negative resistance of InP devices are larger than those of Si devices in case of symmetrical and asymmetrical diodes. Further, the negative resistance profiles in the depletion layer of these diodes exhibit a single peak in the middle of the drift layer in contrast to double peaks in double drift region diodes.     

The hole transport characteristics in SiGe/Si double and triple barrier resonant tunneling structures

Experimental measurements and theoretical calculations have been used to study the hole transport characteristics in SiGe/Si double and triple barrier resonant tunneling structures. The main emphasis is put on discussing the symmetry of I–V characteristics with forward and reverse bias, their temperature dependences and relations to quantum well designs. The calculations show that at current resonance, the sub-level can be much lower (e.g, for heavy hole resonance) or much higher (e.g, for light hole resonance) than the quasi-Fermi-level in the spacer. The distinctly different features of the measured first and second resonances for SiGe/Si double and triple barrier resonant tunneling, can be understood, by considering the different population of the heavy hole and light hole bands in the spacer region and the temperature dependences of Fermi-level, carrier mobility and effective masses. The analysis of dependences of the transmission and I–V curve with quantum well designs presents the possibility of using an asymmetric triple barrier structure to improve the resonant tunneling performance.     

Quantum box resonant tunneling spectroscopy: Experiments and modelisation

We have calculated the potential profile and the electronic levels in resonant tunneling double barrier structures with nanometric lateral dimensions (≤ 500 nm) for various contact doping. At biases for which the box states (laterally confined quantum well) are resonant with the emitter Fermi level, fine structures are expected in the resonant tunneling current. Comparison with I(V) characteristics measured on nanometric GaAs/GaAlAs and GaAs/GaAlAs/InGaAs resonant tunneling diodes shows that our model accounts for the resonance bias voltage and explains the shape of the current peak. The fine structure observed in the current peak provides a spectroscopy of the confined states in the quantum box.     

Numerical study of performance characteristics of deep violet InGaN DQW laser diodes with AlInGaN quaternary multi quantum barrier electron blocking layer

The performance characteristics of deep violet In_0.082Ga_0.918N/GaN double quantum well (DQW) laser diodes (LDs) with different electron blocking layer (EBL) including a ternary AlGaN bulk EBL, a quaternary AlInGaN bulk EBL and ternary AlGaN multi quantum barrier (MQB) EBL has been numerically investigated. Inspired by the abovementioned structures, a new LD structure with a quaternary AlInGaN MQB EBL has been proposed to improve the performance characteristics of the deep violet InGaN DQW LDs. Simulation results indicated that the LD structure with the quaternary AlInGaN MQB EBL present the highest output power, slope efficiency and differential quantum efficiency (DQE) and lowest threshold current compared with the above mentioned structures. They also indicated that choosing an appropriate aluminum (Al) and indium (In) composition in the quaternary AlInGaN MQB layers could control both piezoelectric and spontaneous polarizations. It will decrease the electron overflow from the active region to p-side and increased the contribution of electron and hole carriers to the radiative recombination effectively. Enhancing radiative recombination in the well using the quaternary AlInGaN MQB EBL also increased the optical output power and optical intensity.     

Properties of (InGa)As/GaAs QW (λ ≈ 1.2 µm) facet-coated edge emitting diode laser

In this paper, we report on the design and optical properties of laser diodes with an emission wave-length of ～1170 nm based on an (InGa)As/GaAs double quantum well active layer. The back and front facet of the laser diodes were coated with SiO_x dielectric films that influence the output optical power by enhancing or lowering the facet reflectivity. The measurements show improvement of the facet-coated laser diode properties in the threshold-current-density reduction along with light output power enhancement. Furthermore, a narrow far field pattern and high side mode suppression have been observed.     

Theoretical performance of novel multipliers at millimeter and submillimeter wavelengths

A theoretical comparison of various low and high order multipliers for 200 GHz and 1 THz has been carried out. Novel diodes including single barrier varactors, barrier-intrinsic-n⁺ diodes and high electron mobility varactors are shown to have excellent theoretical performance, comparable or better than the conventional Schottky varactors for single and double diode frequency multipliers at millimeter and submillimeter wavelengths, whereas quantum well diodes, since they suffer from high resistive losses, are shown to be less attractive. In comparison to the conventional Schottky varactor, these new diodes have some potential advantages in their characteristics such as nonlinearity or a special symmetry. For future optimization some general comments on these advantages as well as other factors affecting multiplication is given.     

Lifetime of nonequilibrium charge carriers in the base of <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis>-junction semiconductor diode at arbitrary injection levels

In the approximation of exponential distribution of nonequilibrium charge carriers in the base of semiconductor p-n-junction diode a formula is obtained for lifetime calculation, which is valid at arbitrary injection levels. The lifetime is determined via measurements of only stationary characteristics of diodes (dc-CVC and low-frequency differential resistance). These characteristics, as well as the dependence of the barrier capacity on the reverse voltage, for determination of equilibrium concentration of carriers in the diode base, have been measured for D226B alloy diodes. The dependence of the lifetime of nonequilibrium carriers on the injection level, calculated from experimental data, agrees with the Shockley-Read theory of recombination; this agreement may be considered as a justification of assumptions made for lifetime calculation.     

A theoretical study of resonant tunneling characteristics in triangular double-barrier diodes

Resonant tunneling characteristics of triangular double-barrier diodes have been investigated systematically in this Letter, using Airy function approach to solve time-independent Schrödinger function in triangular double-barrier structures. Originally, the exact analytic expressions of quasi-bound levels and quasi-level lifetime in symmetrical triangular double-barrier structures have been derived within the effective-mass approximation as a function of structure parameters including well width, slope width and barrier height. Based on our derived analytic expressions, numerical results show that quasi-bound levels and quasi-level lifetime vary nearly linearly with the structure parameters except that the second quasi-level lifetime changes parabolically with slope width. Furthermore, according to our improved transmission coefficient of triangular double-barrier structures under external electric field, the current densities of triangular double-barrier diodes with different slope width at 0 K have been calculated numerically. The results show that the N-shaped negative differential resistance behaviors have been observed in current–voltage characteristics and current–voltage characteristics depend on the slope width.     

Multiple wavelength electroluminescence and laser generation in p-i-n resonant tunneling heterostructures

We report a design and electroluminescence (EL) investigation of a p-i-n resonant tunneling device based on an Al_0.4Ga_0.6As/GaAs graded-index waveguide heterostructure. The intrinsic region of the structure consists of a quantum well (QW) surrounded by multiple barrier energy filters providing simultaneous resonant occupation of electron and heavy-hole second excited subbands in the QW. Several peaks are observed in the EL spectra, confirming occupation of the excited subbands. The EL efficiency displays a resonant behavior accompanied by an S-shaped negative differential resistance region in the voltage–current characteristic. Current bistability is demonstrated, leading to bistability in the EL and laser generation spectra.     

Coulomb blockade and coherent single-cooper-pair tunneling in single Josephson junctions

We have measured the current-voltage characteristics of small-capacitance single Josephson junctions at low temperatures ( T< or =0.04 K), where the strength of the coupling between the single junction and the electromagnetic environment was controlled with one-dimensional arrays of dc SQUIDs. We have clearly observed Coulomb blockade of Cooper-pair tunneling and even a region of negative differential resistance, when the zero-bias resistance of the SQUID arrays is much higher than the quantum resistance h/e(2) approximately 26 kOmega. The negative differential resistance is evidence of coherent single-Cooper-pair tunneling in the single Josephson junction.     

ZnCdSe量子阱/CdSe量子点耦合结构中的激子隧穿过程

用室温光致发光谱和飞秒脉冲抽运探测方法对不同垒宽的ZnCdSe量子阱/ZnSe/CdSe 量子点新型耦合结构中激子隧穿过程进行研究，观察到激子从量子阱到量子点的快速隧穿过 程.在ZnSe垒宽为10nm, 15nm, 20nm时，测得激子隧穿时间分别为1.8ps, 4.4ps, 39ps. 关键词： ZnCdSe量子阱 CdSe量子点 激子 隧穿     

InGaN/GaN laser diode characterization and quantum well number effect

The effect of quantum well number on the quantum efficiency and temperature characteristics of In- GaN/GaN laser diodes （LDs） is determined and investigated. The 3-nm-thick In0.13Ca0.87N wells and two 6-am-thick GaN barriers are selected as an active region for Fabry-Perot （FP） cavity waveguide edge emitting LD. The internal quantum efficiency and internal optical loss coefficient are extracted through the simulation software for single, double, and triple InGaN/GaN quantum wells. The effects of device temperature on the laser threshold current, external differential quantum efficiency （DQE）, and output wavelength are also investigated. The external quantum efficiency and characteristic temperature are improved significantly when the quantum well number is two. It is indicated that the laser structures with many quantum wells will suffer from the inhomogeneity of the carrier density within the quantum well itself which affects the LD performance.