The p-n junction quantum well APD: A new solid-state photodetector for lightwave communications systems and on-chip detector applications

A novel variation on the doped quantum well avalanche photodiode is presented that provides comparable signal-to-noise performance at more realizable material doping requirements. The device consists of repeated unit cells formed from a p-n Al0.48In0.52As junction immediately followed by near-intrinsic Ga0.47In0.53As and Al0.48In0.52As layers. As in the doped quantum well device, the asymmetric unit cell selectively heats the electron distribution much more than the hole distribution prior to injection into the narrow-gap Ga0.47In0.53As layer in which impact ionization readily occurs. The effects of various device parameters, such as the junction doping, Ga0.47In0.53As and intrinsic Al0.48In0.52As layer widths as well as the overall bias on the electron and hole ionization rates, is analyzed using an ensemble Monte Carlo method. From the determination of the ionization rates and the ionization probabilities per stage, P and Q, an optimal device design can be obtained that provides high gain at low multiplication noise. In addition, a structure that operates at less than 5 V bias is presented that can provide moderate gain at very low noise. It is expected that the device designs presented herein can serve either as high-gain low-noise detectors for lightwave communications systems or as moderate-gain low-noise detectors for on-chip application.     

Theory of the GaInAs/AlInAs-doped quantum well APD: A new low-noise solid-state photodetector for lightwave communication systems

We present calculations of the electron and hole ionization coefficients, the excess noise factor, and gain for a doped quantum well APD made from the Al0.48In0.52As/Ga0.47In0.53As material systems. The ionization rates are calculated based on an ensemble Monte Carlo method. The effect of all of the device parameters, i.e., doping concentrations, layer widths, and the overall dc bias field, on the carrier ionization coefficients and the deterministic ionization probabilities,PandQ, is determined. These results in conjunction with recent noise theory results are utilized to determine an optimal device design that provides high gain at very low noise. A complete design including number of stages and individual stage design is presented for the lowest noise, highest gain device realizable in this system. It is anticipated that this device can be used as a new ultralow-noise high-gain receiver in lightwave communications systems.     

Theoretical study of multiquantum well avalanche photodiodes made from the GaInAs/AlInAs material system

We present numerical calculations of the electron and hole impact ionization coefficients in bulk Ga0.47In0.53As, Al0.48In0.52As and related multiquantum well structures. It is found that significant enhancement of the electron impact ionization rate over the hole impact ionization rate can be achieved by more than an order of magnitude in simple multiquantum well APD's at low applied electric fields, but only at the expense of severe carrier trapping effects. At large applied fields, ∼ 200 kV/cm, trapping becomes insignificant but the hole ionization rate increases dramatically. An alternative device that has a graded region at the end of the well, grown using a SLAM superlattice structure, is examined. In this structure electron trapping effects are eliminated, but hole trapping can still occur. It is determined that the graded structure shows an improvement over the simple multiquantum well device. The improvement may not be substantial enough to warrant the more complicated development of the graded superlattice device.     

Comparison of multiquantum well, graded barrier, and doped quantum well GaInAs/AlInAs avalanche photodiodes: A theoretical approach

A comparison of the multiquantum well; graded barrier, and doped quantum well Ga0.47In0.53As/Al0.48In0.52As avalanche photodiodes (APD's) is presented based on the calculated gain, excess noise factor, bandwidth, and gain-bandwidth product. A general numerical method, based on an ensemble Monte Carlo calculation, is used to determine the device performance, measured in terms of the electron and hole ionization probabilities, as a function of the device geometries and applied electric field. From a determination of the ionization rates, critical performance figures such as the gain, excess noise factor, and bandwidth can be determined. Various device geometries are examined (different layer widths, dopings, and overall applied electric field strength) among the three device types. The results indicate that the doped quantum well device gives the largest gain-bandwidth product at the lowest noise factor of the three device types. Surprisingly, the highest absolute gain is achievable in a simple multiquantum well APD, but at a much smaller bandwidth than in a doped quantum well device. At comparable device sizes, the doped quantum well device can deliver roughly two orders of magnitude more gain and gain-bandwidth product than either the simple multiquantum well or graded barrier device.     

The p-n heterojunction quantum well APD: A new high-gain low-noise high speed photodetector suitable for lightwave communications and digital applications

A new Ga0.47In0.53As/Al0.48In0.52As multiquantum well avalanche photodiode, the APD, is presented that provides comparable signal-to-noise performance compared to either the doped quantum well APD or the p-n junction quantum well APD, but without carrier trapping effects even at very low overall applied electric fields. The device is made of repeated unit cells consisting of a p-n junction formed between two dissimilar materials followed by a nearly intrinsic wide-bandgap layer. As in the doped quantum well device, the asymmetric unit cell selectively heats the electron distribution much more than the hole distribution within the narrow-gap Ga0.47In0.53As layer leading to a greatly enhanced electron-to-hole ionization rates ratio. The most significant improvement over the doped and p-n junction quantum well devices is the lack of carrier trapping at the heterojunction without further engineering of the interface (compositional grading). Carrier trapping is avoided, thereby providing very high-speed performance even for low-voltage devices, by doping the narrow-gap layer. The resulting built-in field within the GaInAs layer is sufficiently large of itself that both electrons and holes are heated to energies large enough to overcome the potential barrier at the end of the quantum well. In this way, devices operating at 5 V bias can be built that will provide a gain of about 4 at large bandwidths, ~18 GHz.     

Theory of the doped quantum well superlattice APD: A new solid-state photomultiplier

A new superlattice avalanche photodiode structure consisting of repeated unit cells formed from a p-i-n Al0.45Ga0.55As region immediately followed by near intrinsic GaAs and Al0.45Ga0.55As layers is examined using an ensemble Monte Carlo calculation. The effects of various device parameters, such as the high-field layer width, GaAs well width, low-field AlGaAs layer width, and applied electric field on the electron and hole ionization coefficients is analyzed. In addition, the fraction of electrons which ionize in a spatially deterministic way, at the same place in each stage of the device, is determined. As is well known, completely noiseless amplification can be achieved if each electron ionizes in each stage of the device at precisely the same location while no holes ionize anywhere within the device. A comparison is made between the doped quantum well device and other existing superlattice APD's such as the quantum well and staircase APD's. It is seen that the doped quantum well device most nearly approximates photomultiplier-like behavior when applied to the GaAs/AlGaAs material system amongst the three devices. In addition, it is determined that none of the devices, when made from GaAs and AlGaAs, fully mimic ideal photomultiplier-like performance. As the fraction of electron ionizations per stage of the device is increased, through variations in the device geometry and applied electric field, the hole ionization rate invariably increases. It is expected that ideal performance can be more closely achieved in a material system in which the conduction band edge discontinuity is a greater fraction of the band gap energy in the narrow-band gap semiconductor.     

Electron and hole impact ionization rates in InP/Ga0.47In0.53As superlattice

The electron and hole impact ionization rates, α andβ, in an InP/Ga0.47In0.53As superlattice have been experimentally determined from photomultiplication data made on an InP/GaInAs superlattice photodiode. A Monte Carlo simulation of α and β in the superlattice has been developed, and the enhancement of impact ionization due to the effect of the band edge discontinuity has been investigated. The experimental ionization rates have been analyzed by the simulation. The larger β than α in the superlattice has been shown to be explained by the valence band discontinuity about two times larger than the conduction band edge discontinuity in this superlattice structure.     

Monte Carlo simulation of impact ionization rates in InAlAs-InGaAssquare and graded barrier superlattice

The Monte Carlo method is used to analyze impact ionization rates for electrons and holes in a 〈100〉 crystal direction In_0.52Al_0.48As-In_0.53Ga_0.47 As square and graded barrier superlattice. The calculated impact ionization rate ratio α/β is enhanced to more than 10 in a wide barrier and narrow-well square barrier superlattice. This is because the hole ionization rate β is greatly reduced in the narrower well superlattice, while the electron ionization rate α is less sensitive to well and barrier layer thickness. These results are explained by a combination of the ionization dead space effect for the barrier layer and the electron ionization rate enhancement in the well layer due to large conduction band edge discontinuity. Furthermore, it is found that in a graded barrier superlattice, the impact ionization rate ratio α/β is smaller than that for a square barrier superlattice having the same barrier and well thickness. This is due to the occurrence of hole ionization in the narrow bandgap region in graded barriers. The band structure effects on hot carrier energy distribution, as well as impact ionization, are also discussed     

Compound semiconductors for low-noise microwave MESFET applications

In order to determine the low-noise potential of microwave MESFET's fabricated from materials other than GaAs, a one-dimensional FET model is employed. From material parameters and device geometry the model enables the calculation of a small-signal equivalent circuit from which performance information is acquired. Material parameters, as predicted from Monte Carlo calculations, are used to simulate 1-µm devices fabricated from GaAs as well as InP, Ga0.47In0.53As, InP0.8As0.2, Ga0.27In0.73P0.4As0.6, and Ga0.5In0.5As0.96Sb0.04. Results obtained from simulations comparing a Ga0.5In0.5As0.96- Sb0.04device to an equivalent GaAs device indicate that a decrease in minimum noise figure of almost a factor of two is possible. Considerable improvement in noise performance over a GaAs device is also predicted for devices fabricated from Ga0.47In0.53As and Ga0.27In0.73P0.4As0.6. In addition, the quaternary and ternary devices as well as the InP device should exhibit superior gain and high-frequency performance compared to GaAs devices.     

Theoretical analysis of confined quantum state GaAs/AlGaAssolid-state photomultipliers

A detailed theoretical analysis of the design considerations of a solid-state photomultiplier based on avalanche multiplication of carriers out of confined quantum states is presented. Since these devices are unipolar, much lower noise and higher speed of performance are anticipated as compared with interband avalanche photodiodes. As an example of the design criteria for confined-state photomultipliers, a GaAs/Al_0.32Ga_0.68As multiquantum well structure is analyzed as to impact ionization rate, gain, dark current, and multiplied dark current. It is found that the highest gain is achieved in an asymmetric quantum well structure in which the second barrier height is half as large as the initial barrier height. The gain is further evaluated for a symmetric quantum well device. The effects of the applied electric field, quantum well doping concentration, and layer widths on device performance are examined     

A theoretical treatment of the subband population in the intersubband staircase laser

A theoretical study of the subband occupation in an intersubband staircase laser has been performed within the density-matrix approach by applying a canonical transformation to a tight-binding model of a superlattice with four quantum wells per unit cell. The field-induced carrier redistribution in a superlattice structure is investigated, for which recently mid-infrared laser operation has been demonstrated. An intrinsic population inversion occurs, which is due to resonant tunneling.     

Properties of a tunneling injection quantum-well laser: Recipe for`cold' device with a large modulation bandwidth

A quantum-well laser in which electrons are directly injected into the lasing quantum well by resonant tunneling is proposed and demonstrated. The preliminary GaAs-based devices, grown by molecular beam epitaxy have an 80-Å In_0.1Ga_0.9As active single quantum well and AlAs tunneling barriers. I_th is 15 mA in a single-mode ridge device and the differential gain is ~2×10^-16 cm^-2. The principle of operation promises a `cold' laser at high injection levels, and therefore Auger recombination and chirp are expected to be suppressed. In addition, tunneling of carriers into the active well as the potential to achieve large modulation bandwidths     

超晶格雪崩光电二极管

已经提出了几种可以提高载流子离化率比的超晶格雪崩光电管:量子阱雪崩光电管、台阶型雪崩光电管和掺杂量子阱雪崩光电管。这几种器件都主要是利用异质界面带隙突变导致的电子离化几率相对于空穴离化几率的显著增大,从而可以获得低的雪崩噪声和高的增益—带宽乘积。本文概述了这几种器件的结构、工作原理以及结构参量对器件性能的影响。     

Gain and the threshold of three-dimensional quantum-box lasers

Gain and threshold current density are analyzed for quantum-box lasers where electrons are confined in quantum well three-dimensionally, based on the density-matrix theory of semiconductor lasers with relaxation broadening. The electronic dipole moment and its polarization dependence are first analyzed, and it is shown that the gain becomes maximum when the electric field of light is parallel to the longest side of the quantum box. Calculated gain is about 10 times that of bulk crystal for 100 Å × 100 Å × 100 Å GaAs/Ga0.8Al0.2As quantum box, and 15 times for Ga0.47In0.53As/InP quantum box with the same size, respectively. The threshold current density are 45 A/cm²and 62 A/cm²for GRINSCH GaAs/(Ga0.8Al0.2As-Ga0.4Al0.6As) and Ga0.47In0.53As/(Ga0.28In0.72As0.6P0.4-InP), respectively, where for the GaInAs/ GaInAsP/InP system the intervalence band absorption and nonradiative recombinations have been assumed to be the same as those obtained for bulk crystals experimentally. These results show the possibility of remarkable reduction in the laser threshold by the quantum-box structures.     

新型电子器件和光学器件的共振隧穿结构

描述了一种新型共振隧穿结构器件，这种器件包含了通过可变间隙超晶格能量滤波器（ＶＳＳＥＦ）中的耦合量子附态的隧穿过程．论证了通过ＡｌＡｓ／ＧａＡｓＶＳＳＥＦ器件高能态和ＡｌＧａＡｓ／ＧａＡｓ超晶格受激态的共振隧穿，描述了这种器件作为较高功率微波源和共振隧穿晶体管的应用，并讨论了共振隧穿结构作为雪崩探测器和红外发射器等光学器件的潜在应用．     

Counting distributions and error probabilities for optical receivers incorporating superlattice avalanche photodiodes

Exact gain distributions and electron counting distributions are presented for superlattice avalanche photodiodes that operate by single-carrier transport perpendicular to the superlattice planes. The characteristic shapes of these distributions are compared with those of the single-carrier conventional avalanche photodiode and the photomultiplier tube. The electron counting distributions, which assume Poisson photocarrier injection, are used to calculate the error performance of a simple optical communication system. This performance is compared with that achievable by a single-carrier conventional APD receiver of identical quantum efficiency and gain. For simplicity of calculation, the system consists of a transmitter emitting light pulses containing a Poisson number of photons and a maximum-likelihood integrate-and-dump receiver. It makes use of binary on-off keying and is subject to noise events arising from multiplied background radiation and/or multiplied dark noise. The performance of the superlattice photodiode receiver turns out to be always superior to that of the single-carrier conventional photodiode receiver, for all values of the gain. The advantage can attain several orders of magnitude (even though the excess noise factors for the two devices lie within a factor of two). The superlattice receiver with high impact-ionization probability is shown to behave like an ideal photon counter with the same quantum efficiency, even if the device has many stages. The deleterious effects of receiver thermal noise on probability of error are examined.     

Monte Carlo simulation of gain compression effects in GRINSCHquantum well laser structures

Gain compression is widely acknowledged to be a serious limitation to the ultimate modulation bandwidth of a semiconductor laser. We have developed a numerical technique to study the gain compression effects in graded-index separate confinement heterostructure (GRINSCH) quantum well laser structures, This technique is based on the combination of the Monte Carlo simulation of the carrier dynamics in the device while under intense stimulated photon emission, and the calculation of the optical gain using a 4×4 k·p Hamiltonian. From the simulated results, we calculated a gain compression coefficient ϵ=1.1×10^-17 cm³ for a linearly graded quantum well laser structure having a 50 Å In_0.2Ga_0.8As well. We find good agreement between our results and published experiments. We have also demonstrated that our calculation method is capable of simulating the gain dynamics in the laser structure, such as those studied with femtosecond pump-probe experimental techniques     

Resonant tunneling transistors with controllable negative differential resistances

Three-terminal devices based on resonant tunneling through two quantum barriers separated by a quantum well are presented and analyzed theoretically. Each proposed device consists of a resonant tunneling double barrier heterostructure integrated with a Schottky barrier field-effect transistor configuration. The essential feature of these devices is the presence, in their output current-voltage (I_{D} - V_{D}) curves, of negative differential resistances controlled by a gate voltage. Because of the high-speed characteristics associated with tunnel structures, these devices could find applications in tunable millimeter-wave oscillators, negative resistance amplifiers, and high-speed digital circuits.     

Ga0.47In0.53As: A ternary semiconductor for photodetector applications

Ga0.47In0.53As has been used to make fast (rt < 1 ns), photodiodes with low dark current (i_{D} < 10^{-8}A) and good quantum efficiency (ηQext > 50 percent over the entire1.0-1.7 mum region of the optical spectrum). The physical properties related to the crystal growth and carrier transport are discussed in this paper in terms of both the design and the operating characteristics of detectors fabricated from this ternary alloy. The results of our work show that Ga0.47In0.53As is a material well-suited to several important semiconductor device applications. A comparison to other semiconductor photodiodes shows that Ga0.47In0.53As is one of the most sensitive detectors available in the1.0-1.7 mum wavelength region. One can expect repeater-free transmission in excess of 150 km at 100 Mbits . s^-1using these detectors in a digital optical fiber link at the 1.55 μm low-loss (alpha < 0.3dB . km^-1) low-dispersion transmission window.     

超晶格雪崩光电二极管的结构优化及性能研究

基于碰撞离化理论研究了异质材料超晶格结构对载流子离化率的作用,设计得到In0.53Ga0.47As/In0.52Al0.48As超晶格结构的雪崩光电二极管。通过分析不同结构参数对器件性能的影响,得到了低隧道电流、高倍增因子的超晶格结构雪崩层,根据电场分布方程模拟了器件二维电场分布对电荷层厚度及掺杂的依赖关系,并优化了吸收层的结构参数。对优化得到的器件结构进行仿真并实际制作了探测器件,进行光电特性测试,与同结构普通雪崩光电二极管相比,超晶格雪崩光电二极管具有更强的光电流响应,在12.5~20 V的雪崩倍增区,超晶格雪崩光电二极管在具备高倍增因子的同时具有较低的暗电流,提高了器件的信噪比。