Double junction AlInAs/GaInAs multiquantum well avalanche photodiodes

A separate absorption, grading, and multiplication avalanche photodiode with an AlInAs/GaInAs multiquantum well multiplication region is reported. This device exhibits a low excess-noise factor and a gain-bandwidth product of 50 GHz, due to the high ratio of ionisation rates of the multiplication material. In addition, a large bandwidth is obtained owing to the use of an undoped (n type) GaInAs absorption layer, fully depleted when multiplication occurs.<>     

High-speed GaInAs/InP multiquantum well avalanche photodiodes grownby atmospheric-pressure MOCVD

Reports the performance of the first high speed GaInAs/InP multi-quantum well avalanche photodiodes grown by atmospheric pressure MOCVD. The multi-quantum well avalanche region of the device consists of 50 periods of 150 Å wells and barriers forming the intrinsic region of a pin structure. Avalanche multiplication up to a factor of 25 has been measured at DC together with high-speed response giving a maximum measured RF gain of 16 and a gain-bandwidth product in excess of 25 GHz     

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.     

Investigation of guardring-free planar AlInAs avalanche photodiodes

We analyze the operation principle and the characteristics of a guardring-free planar AlInAs avalanche photodiode (APD) by computational simulation and experimental results. The simple planar structure is based on a novel epitaxy-junction diode concept and its practical performance for 10-Gb/s optical receivers was successfully demonstrated. Electric field simulations clarified how edge multiplication, which is an inherent problem in APDs, is suppressed in the guardring-free structure. The experimental results, which are current-voltage, capacitance-voltage, and wide-range line scans of responsivity, support the simulation results, and the simulation explains the peculiar characteristics of the experimental results. The computational and the experimental analysis are consistent with one another.     

Excess noise design of InP/GaInAsP/GaInAs avalanche photodiodes

An InP/GaInAsP/GaInAs avalanche photodiode (APD) with separate absorption and multiplication (SAM) regions has been designed taking into account the excess noise generated in GaInAsP and GaInAs. The multiplication factor dependence of the excess noise factorFhas been calculated using realistic electron and hole ionization rates in InP, GaInAsP, and GaInAs, assuming that the avalanche multiplication occurs not only in InP but in GaInAsP and GaInAs. The calculatedFvalues have been compared to the experimental ones measured on a planar-type InP/GaInAsP/GaInAs APD for illumination at a wavelength of 1.3 μm. It has been found the the calculated excess noise agrees very well with the experimental measurements. The limited ranges of device parameters in which the conditions of minimal excess noise, tunneling current, and charge pile-up are satisfied have been obtained. We conclude that the excess noise generated in GaInAsP and GaInAs should be considered in a practical device design.     

A model-based comparison of AlInAs/GaInAs and InP/GaInAs HBT's: aMonte Carlo study

The high-speed performances of AlInAs/GaInAs and InP/GaInAs heterojunction bipolar transistors (HBTs) are investigated using a one-dimensional self-consistent particle simulator. Optimum alloy compositions for a graded-gap base structure are obtained for both transistors through the tradeoff between the emitter-charging time and base transit time. The saturation velocity in the GaInAs n-type collector is found to be smaller than that in InP, which has been attributed to the diffusion of a large number of hot back-scattered Γ-valley electrons in the GaInAs collector. The difference in the collector transit time in p-type collectors is trivial, since the maximum electron velocity was restricted to below 1.2×10⁸ cm/s due to a strong nonparabolicity effect. The cutoff frequency for the former and the latter are estimated to be 2 and 1.5 times higher, respectively, than for AlGaAs/GaAs HBTs. These results are attributed to a larger bandgap difference between the emitter and base, to yield a high base built-in field, rather than a larger Γ-L band separation energy in the collector to enhance the velocity overshoot effect     

Fabrication of electroabsorption optical modulators using laserdisordered GaInAs/GaInAsP multiquantum well structures

Electroabsorption optical modulators have been fabricated on GaInAs/GaInAsP multiquantum well structures whose bandgap had been increased by laser photoabsorption-induced disordering. Modulation depths of 20 dB have been obtained in material which has been bandgap blue shifted by as much as 120 nm, while samples shifted by 80 nm gave depths as high as 27 dB     

Reliability of AlInAs/GaInAs heterojunction bipolar transistors

The reliability of high-performance AlInAs/GaInAs heterojunction bipolar transistors (HBTs) grown by molecular beam epitaxy (MBE) is discussed. Devices with a base Be doping level of 5×10¹⁹ cm^-3 and a base thickness of approximately 50 nm displayed no sign of Be diffusion under applied bias. Excellent stability in DC current gain, device turn-on voltage, and base-emitter junction characteristics was observed. Accelerated life-test experiments were performed under an applied constant collector current density of 7×10⁴ A/cm² at ambient temperatures of 193, 208, and 328°C. Junction temperature and device thermal resistance were determined experimentally. Degradation of the base-collector junction was used as failure criterion to project a mean time to failure in excess of 10⁷ h at 125°C junction temperature with an associated activation energy of 1.92 eV     

Theoretical study of the threshold characteristics of InGaN multiquantum well lasers

The threshold characteristics of InGaN multiquantum well lasers are investigated. A detailed analysis of the dependence of the threshold current on the quantum-well parameters and the temperature is performed. It is shown that, in comparison with long-wavelength lasers, InGaN lasers have a qualitatively different dependence of the threshold current on the quantum-well parameters (well width and number of quantum wells). The possibility of optimizing a InGaN laser structure is analyzed with the aim of improving the threshold characteristics and increasing the peak radiated power. Fiz. Tekh. Poluprovodn. 32, 843–848 (July 1998)     

Parametric manufacturing yield modeling of GaAs/AlGaAs multiplequantum well avalanche photodiodes

GaAs/AlGaAs multiple quantum well (MQW) avalanche photodiodes (APD's) are of interest as an ultra-low noise image capture mechanism for high-definition systems. Since literally millions of these devices must be fabricated for imaging arrays, it is critical to evaluate potential performance variations of individual devices in light of the realities of semiconductor manufacturing. Specifically, even in a defect-free manufacturing environment, random variations in the fabrication process will lead to varying levels of device performance, Accurate device performance prediction requires precise characterization of these variations. This paper presents a systematic methodology for modeling the parametric performance of GaAs MQW APD's. The approach described requires a model of the probability distribution of each of the relevant process variables, as well as a second model to account for the correlation between this measured process data and device performance metrics. The availability of these models enables the computation of the joint probability density function required for predicting performance using the Jacobian transformation method. The resulting density function can then be numerically integrated to determine parametric yield. Since they have demonstrated the capability of highly accurate function approximation and mapping of complex, nonlinear data sets, neural networks are proposed as the preferred tool for generating the models described above. In applying this methodology to MQW APD's, it is shown that using a small number of test devices with varying active diameters, barrier and well widths, and doping concentrations enables prediction of the expected performance variation of APD gain and noise in larger populations of devices. This approach compares favorably with Monte Carlo techniques and allows device yield prediction prior to high volume manufacturing in order to evaluate the impact of both design decisions and process capability     

Theoretical investigation of quantum-dot avalanche photodiodes for mid-infrared applications

A novel midinfrared sensor, called the quantum-dot avalanche photodiode (QDAP), is proposed which is expected to have improved signal-to-noise ratio (SNR) in the presence of Johnson noise over its quantum-dot (QD) counterpart. In the QDAP, an intersubband QD detector is coupled with a thin, low-noise GaAs avalanche layer through a tunnel barrier. The avalanche layer provides the necessary photocurrent gain required to overcome Johnson noise and nearly achieve the dark-current-limited SNR of the QD detector. In the proposed three-terminal device, the applied biases of the QD-detector and the avalanche-photodiode sections of the QDAP are controlled separately. This feature permits the control of the QDs responsivity and dark current independently of the operating avalanche gain, thereby allowing the optimization of the avalanche multiplication factor to maximize the photocurrent's SNR. Notably, a heterojunction potential-barrier layer can also be utilized to further improve the SNR. For example, when the standard deviation of the Johnson noise is four times greater than the dark current, calculations show that the SNR enhancement offered by an avalanche multiplication factor of 5 results in relaxing the cooling requirement from 20 to 80 K.     

Low-frequency noise characteristics of AlInAs/GaInAs modulation-doped field-effect transistors

The output noise voltage of AlInAs/GaInAs MODFETs grown by both MOCVD and MBE was measured at frequencies from 1 MHz to 1.5 GHz under different bias conditions for the first time. For frequencies below 500 MHz the noise voltage showed a 1/f dependence with a corner frequency around 200 MHz. The low-frequency noise was larger at the bias conditions giving higher transconductance.<>     

GaInAs／AlInAs调制掺杂结构材料的光学性质研究

研究了ＧａＩｎＡｓ／ＡｌＩｎＡｓｎ型调制掺杂结构样品的光致发光及其激发光谱。当空穴态被局域化后．二维电子气的发光线形反映了导带二维态密度的填充效应：导带两个子带填充电子。发光强度则表明，导带第二子带电子波函数在空间上更扩展，与空间分离的空穴产生发光复合的几率较大。激发光谱提供了样品中异质结结构直接带边附近光吸收过程的信息。     

GaInAs/AlInAs量子阱激光器特性--价带间光吸收对微分量子效率和特征温度的影响

计算和分析了晶格匹配ＧａＩｎＡｓ／ＡｌＩｎＡｓ半导体量子阱激光器（ＱＷＬ）中的价带间光吸收系数及其对微分量子效率（η０）和特征温度（Ｔ０）的影响。结果表明,价带间光吸收系数随带隙增加而减小,随温度和载流子浓度增加而增加,其所引起的阈值和出光微分量子效率的变化趋势虽然与实验观察到的相类似,但数值上却不起明显的作用。因此,价带间光吸收这种温敏光子损耗机制对长波长半导体激光器的温度效应不可能起主要的作用。     

Flip-chip planar GaInAs/InP p-i-n photodiodes analysis of frequencyresponse

High-speed response, high-manufacturing-yield photodiodes will be needed for optical interconnection in computer and for broadband networks. Frequency responses of a new planar GaInAs/lnP p-i-n photodiode for flip-chip bonding are analyzed. To study changes caused by the new structure, responses are related to device parameters including photoabsorption layer thickness, p-i-n junction diameter, and the size of the forward biased p-i-n junction. Forward biasing is a peculiarity of our photodiodes. A photodiode with an optimized design showed good characteristics     

GaInAs/AlInAs多量子阱结构光学性质的研究

我们研究了与InP衬底晶格匹配的GaInAs/AlInAs三元材料多量子阱异质结构的光学性质,测量了不同阱宽量子阱在低温下的吸收光谱、光致发光及其激发光谱,以及吸收光谱随温度的变化.所测样品的光致发光峰主要取决于与缺陷态有关的跃迁过程,但吸收光谱中直到室温仍观察到重轻空穴的本征激子峰.吸收光谱线形明显地反映了多量子阱中电子态的二维特性.对不同量子阱中各子带间跃迁能量因温度上升而产生的红移进行了测定和分析.用Kronig-Penney模型对子带能量所作的计算表明,为了与测量到的跃迁能量获得满意的拟合,必须在计算中计入导带和价带的非抛物线性效应.我们结合光学性质和X光双晶衍射测量,对层厚、应变和组份均匀性等样品结构参量进行了分析.     

A study of low-bias photocurrent gradient of avalanche photodiodes

Presents a study of the photo-response of avalanche photodiodes (APDs) under low reverse bias at unity gain. Some wafers exhibit a linear increase of photocurrent as a function of bias voltage; the "slope" of this linear current-voltage (I-V) curve has been examined under different illumination conditions, fabrication procedures and growth conditions. The observed characteristics are explained in terms of the extension of the depletion region edge toward the surface. An analytical model, based on minority drift-diffusion and current continuity equations, provides good fits to the experimental results for small (/spl sim/0.1 /spl mu/m) "effective diffusion lengths.".     

Frequency response of InP/InGaAsP/InGaAs avalanche photodiodes

A theoretical model for the frequency response of InP/InGaAs avalanche photodiodes (APDs) is presented. Included in the analysis are resistive, capacitive, and inductive parasitics, transit-time factors, hole trapping at the heterojunction interfaces, and the avalanche buildup time. The contributions of the primary electrons, primary holes, and secondary electrons to the transit-time-limited response are considered separately. Using a measurement apparatus which consists of a frequency synthesizer and a spectrum analyzer controlled by a microcomputer, the frequency response of InP/InGaAsP/InGaAs APDs grown by chemical-beam epitaxy are measured. Good agreement with the calculated response has been obtained over a wide range of gains     

Liquid-phase-epitaxial growth of Inp/InGaAsP/InGaAs buried-structure avalanche photodiodes

An InP/InGaAsP/InGaAs avalanche photodiode with an effective guard-ring structure has been successfully fabricated. The diode has a planar structure with an n-InP layer buried by n?-InP in the multiplication region The structure has been grown on a (111)A-oriented InP substrate by two-step growth of liquid-phase epitaxy. Prior to the second growth of n?-InP a meltback technique was used to reduce dark current.