Optimum design of δ-doped InGaAs avalanche photodiode byusing quasi-ionization rates

An avalanche photodiode (APD) designed by using quasi-ionization rates in InP and InGaAs is described. The structure has a δ-doped layer in an InP window layer. The heterointerface electric field is investigated and determined to prevent the tunneling current and carrier multiplication in InGaAs. The gain bandwidth (GB) product of the δ-doped APD is analyzed by R.B. Emmons's (1967) p-i-n electric field method. The highest GB product is 160 GHz     

Excess noise in GaAs avalanche photodiodes with thin multiplicationregions

It is well known that the gain-bandwidth product of an avalanche photodiode can be increased by utilizing a thin multiplication region. Previously, measurements of the excess noise factor of InP-InGaAsP-InGaAs avalanche photodiodes with separate absorption and multiplication regions indicated that this approach could also be employed to reduce the multiplication noise. This paper presents a systematic study of the noise characteristics of GaAs homojunction avalanche photodiodes with different multiplication layer thicknesses. It is demonstrated that there is a definite “size effect” for multiplication regions less than approximately 0.5 μm. A good fit to the experimental data has been achieved using a discrete, nonlocalized model for the impact ionization process     

An InGaAs/InAlAs superlattice avalanche photodiode with a gain bandwidth product of 90 GHz

The authors describe the fabrication of an InGaAs/InAlAs superlattice avalanche photodiode with a gain-bandwidth product of 90 GHz. The device is composed of an InGaAs/InAlAs superlattice multiplication region and an InGaAs photoabsorption layer. The effect of the superlattice multiplication region thickness on the gain-bandwidth product was studied. A gain-bandwidth product of 90 GHz was obtained for the device with a multiplication region thickness of 0.52 mu m. Low noise performance is compatible with the high gain-bandwidth product due to improvement of the ionization rate ratio made by introducing a superlattice structure into the multiplication region.<>     

Performance of thin separate absorption, charge, and multiplicationavalanche photodiodes

Previously, it has been demonstrated that resonant-cavity-enhanced separate-absorption-and-multiplication (SAM) avalanche photodiodes (APDs) can achieve high bandwidths and high gain-bandwidth products while maintaining good quantum efficiency. In this paper, we describe a GaAs-based resonant-cavity-enhanced SAM APD that utilizes a thin charge layer for improved control of the electric field profile. These devices have shown RC-limited bandwidths above 30 GHz at low gains and gain-bandwidth products as high as 290 GHz. In order to gain insight into the performance of these APDs, homojunction APDs with thin multiplication regions were studied. It was found that the gain and noise have a dependence on the width of the multiplication region that is not predicted by conventional models. Calculations using width-dependent ionization coefficients provide good fits to the measured results. These calculations indicate that the gain-bandwidth product depends strongly on the charge layer doping and on the multiplication layer thickness and, further, that even higher gain-bandwidth products can be achieved with optimized structures     

Avalanche buildup time of an InP/InGaAsP/InGaAs APD at high gain

Under a high-gain operating condition, the presence of a multiplication process in the InGaAs(P) regions of an InP/InGaAsP/InGaAs avalanche photodiode (APD) having a structure of separated absorption and multiplication regions could lead to significant enhancement of the avalanche buildup time. As a result, the bandwidth of the device could be reduced considerably. The dependence of the avalanche multiplication factor and the intrinsic response time on the reverse bias voltage, the heterointerface field, the doping concentrations, and the width of the InP layer is examined in detail for the case in which hole injection is assumed. It is shown, for example, that for a fixed value of doping concentrations, reduction of the excess noise factor and enhancement of the gain-bandwidth product of the device can be achieved at the same time by a proper increase of the width of the InP layer     

Detrimental effect of impact ionization in the absorption region on the frequency response and excess noise performance of InGaAs-InAlAs SACM avalanche photodiodes

It is shown that optimization of the electric field profile in the absorption region of separate absorption, charge, and multiplication InGaAs-InAlAs avalanche photodiodes is critical to achieve low excess noise and high gain bandwidth product.     

A p-channel coupled delta-doped silicon MESFET grown by molecularbeam epitaxy

Experimental realization of a new p-channel Si MESFET structure, utilizing two boron δ-doped layers placed in close proximity with one another as the conducting channel, is reported for the first time. This simple homoepitaxially grown Si structure exhibits not only higher sheet carrier density but also higher hole mobility than those of a single δ-doped layer. The measured transconductance of the device is 1.44 mS/mm at 300 K with a gate length of 5 μm, which is a factor of 1.7 higher than the single δ-doped layer Si MESFET for the same dose in each δ-doped layer     

Optimal excess noise reduction in thin heterojunction Al/sub 0.6/Ga/sub 0.4/As-GaAs avalanche photodiodes

It has been recently found that the initial-energy effect, which is associated with the finite initial energy of carriers entering the multiplication region of an avalanche photodiode (APD), can be tailored to reduce the excess noise well beyond the previously known limits for thin APDs. However, the control of the initial energy of injected carriers can be difficult in practice for an APD with a single multiplication layer. In this paper, the dead-space multiplication recurrence theory is used to show that the low noise characteristics associated with the initial-energy effect can be achieved by utilizing a two-layer multiplication region. As an example, a high bandgap Al/sub 0.6/Ga/sub 0.4/As material, termed the energy-buildup layer, is used to elevate the energy of injected carriers without incurring significant multiplication events, while a second GaAs layer with a lower bandgap energy is used as the primary carrier multiplication layer. Computations show that devices can be optimally designed through judicious choice of the charge-layer width to produce excess noise factor levels that are comparable to those corresponding to homojunction APDs benefiting from a maximal initial-energy effect. A structure is presented to achieve precisely that.     

Avalanche noise characteristics of thin GaAs structures withdistributed carrier generation [APDs]

It is known that both pure electron and pure hole injection into thin GaAs multiplication regions gives rise to avalanche multiplication with noise lower than predicted by the local noise model. In this paper, it is shown that the noise from multiplication initiated by carriers generated throughout a 0.1 μm avalanche region is also lower than predicted by the local model but higher than that obtained with pure injection of either carrier type. This behavior is due to the effects of nonlocal ionization brought about by the dead space; the minimum distance a carrier has to travel in the electric field to initiate an ionization event     

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。     

The sensitivity of photoconductor receivers for long-wavelength optical communications

We calculate the sensitivity of In0.53Ga0.47As photoconductor receivers for use in moderate to high bit-rate lightwave transmission applications. It is found that the noise of photoconductive receivers is dominated at all bit ratesB < 4Gbit/s by Johnson noise in the conductive channel. Nevertheless, the total noise current decreases approximately linearly with photoconductive gain, and therefore the sensitivity of photoconductive receivers can be comparable to high-sensitivity p-i-n photodiode receivers. The sensitivity of practical photoconductive receivers compares most favorably with p-i-n receivers in the bit-rate range of 500-2 Gbit/s. However, receivers employing high-speed In0.53Ga0.47As/InP avalanche photodiodes are expected to be more sensitive than photoconductive receivers over the entire bit-rate range considered. In this analysis, we consider the effects of slow photoconductor response on receiver sensitivity, and find that the limited gain-bandwidth product of practical photoconductors increases the complexity of the receiver circuit by necessitating equalization, resulting in a decrease in receiver sensitivity and dynamic range.     

Characteristics of germanium avalanche photodiodes in the wavelength region of 1-1.6 µm

Dark current, quantum efficiency, multiplication noise, and pulse response of germanium avalanche photodiodes with n+-p junction were studied to find an optimum structure. The dark current can be separated by graphical means into a leakage current component and a multiplied component which flows through the junction. The dark current components are also evaluated by using diodes with various diameters. The quantum efficiency and the multiplication noise are shown to be strongly affected by the n+ layer thickness. An n+ layer thickness optimized for signal-to-noise ratio is estimated from experimental and calculated results, using a figure of merit for avalanche photodiodes. The response waveform for mode-locked Nd:YAG laser shows a rise time of 100 ps and a half pulsewidth of less than 200 ps.     

Planar InP-InGaAs avalanche photodetectors with n-multiplicationlayer exhibiting a very high gain-bandwidth product

A planar separate absorption, grading, charge, and multiplication (SAGCM) avalanche photodiode (APD) structure was designed and fabricated, allowing for an updoped multiplication layer without the use of guard rings. A very high gain-bandwidth (GBW) product of 93 GHz and DC gains exceeding 1000 have been measured for a 30-μm-diameter device. This GBW is, to the author's knowledge, the highest reported to date in any III-V APD. In principle, the useful gain-bandwidth product of SAGCM structures is not limited by the tunneling limit in the InP avalanche region of 140 GHz for conventional separate absorption, grading, and multiplication (SAGM) structures     

High-speed photodiode signal enhancement at avalanche breakdown voltage

It has previously been found that when photons are injected into a photodiode biased to the avalanche region, that there is a multiplication of the signal over the usual bias-voltage signal level. This multiplication is due to the created electron-hole pairs colliding with the lattice and creating more electron-hole pairs under the influence of the large biasing field. This paper presents a circuit analysis of this effect when using a high-speed silicon (Si) P-I-N photodiode and shows what the SNR bandwidth and Noise Equivalent Power (NEP) are under both normal bias conditions and avalanche bias conditions. It is shown that there is a substantial improvement in the NEP and SNR ratio at high frequencies when operating at avalanche so that the device may be made nearly shot noise limited if the multiplication factorMis sufficiently large. Microwave measurements on such a high-speed diode gave gains greater than 30 dB with a SNR improvement of 13 dB at 1.45 Gc/s. The effect was observed at frequencies as high as 2.54 Gc/s and appeared to follow a linear 1/M law with bias voltage in the avalanche region with some deviation at large values ofM. The device SNR ratio at moderately high light levels is determined by the signal-to-shot noise ratio. A high modulation depth is found to be essential to reduce shot noise. Analysis of the diode circuit reveals that the detected signal power bandwidth product is a constant. The NEP is found to vary directly with the bandwidth in a pulse type system. Avalanche operation increases the signal power by M²and decreases the NEP byMat high frequencies. The photodiode appears to nearly provide the solid-state analog of the photomultiplier tube.     

GaN基雪崩光电二极管及其研究进展

越来越多的民用与军事对高灵敏度紫外探测的需求促进了GaN基雪崩光电二极管（APD）的快速发展。雪崩光电二极管工作在高反偏电压状态,器件内部载流子在高场下发生碰撞离化,从而使探测信号产生增益。首先对GaN基雪崩光电二极管的研究进展进行了回顾,然后重点报道了器件的增益最大可达3105,介绍了本征层厚度与器件暗电流的关系,简单介绍了正在组建的基于相敏探测的交流增益测试系统,并研究了过剩噪声与调制频率之间的关系,发现在低频波段（30~2kHz）,过剩噪声呈现1/f噪声特性。最后,对盖革模式的雪崩光电二极管的研究进展及应用前景进行了简单介绍。     

Design and analysis of separate-absorption-transport-charge-multiplication traveling-wave avalanche photodetectors

This paper proposes a novel type of avalanche photodiode-the separate-absorption-transport-charge-multiplication (SATCM) avalanche photodiode (APD). The novel design of photoabsorption and multiplication layers of APDs can avoid the photoabsorption layer breakdown and hole-transport problems, exhibit low operation voltage, and achieve ultra-high-gain bandwidth product performances. To achieve low excess noise and ultra-high-speed performance in the fiber communication regime (1.3/spl sim/1.55 /spl mu/m), the simulated APD is Si-based with an SiGe-Si superlattice (SL) as the photoabsorption layer and traveling-wave geometric structures. The frequency response is simulated by means of a photo-distributed current model, which includes all the bandwidth-limiting factors, such as the dispersion of microwave propagation loss, velocity mismatch, boundary reflection, and multiplication/transport of photogenerated carriers. By properly choosing the thicknesses of the transport and multiplication layers, microwave propagation effects in the traveling-wave structure can be minimized without increasing the operation voltage significantly. A near 30-Gb/s electrical bandwidth and 10/spl times/ avalanche gain can be achieved simultaneously, even with a long device absorption length (150 /spl mu/m) and low operation voltage (/spl sim/12 V). In addition, the ultrahigh output saturation power bandwidth product of this simulated TWAPD structure can also be expected due to the large photoabsorption volume and superior microwave-guiding structure.     

Low avalanche noise characteristics in thin InP p+-i-n+ diodes with electron initiated multiplication

We have performed electron initiated avalanche noise measurements on a range of homojunction InP p⁺-i-n⁺ diodes with “i” region widths, w ranging from 2.40 to 0.24 μm. In contrast to McIntyre's noise model a significant reduction in the excess noise factor is observed with decreasing w at a constant multiplication in spite of α, the electron ionization coefficient being less than β, the hole ionization coefficient. In the w=0.24 μm structure an effective β/α ratio of approximately 0.4 is deduced from the excess noise factor even when electrons initiate multiplication, suggesting that hole initiated multiplication is not always necessary for the lowest avalanche noise in InP-based avalanche photodiodes     

Photoconductor receiver sensitivity

The various contributions to photoconductor (PC's) noise are calculated and are used to determine the sensitivity of digital photoconductor receivers for use in lightwave communication systems. We find that Johnson noise is the most significant source of noise current up to bit rates as high as 4 Gbit/s, above which FET channel noise becomes dominant. In comparing the results obtained for ideal photoconductive receivers with receivers employing p-i-n photodetectors, we find that the sensitivities of both circuits are comparable, provided that low-capacitance p-i-n receivers are employed. In contrast, we find that avalanche photodiode receivers have higher sensitivities than either photoconductor or p-i-n receivers over the entire bit-rate range considered. It is concluded that equalization necessary for photoconductor receiver operation at high bit rates due to a limited gain-bandwidth product significantly degrades the sensitivity of the receiver.     

Multiplication noise of wide-bandwidth InP/InGaAsP/InGaAs avalanchephotodiodes

Measurements of InP/InGaAsP/InGaAs separate absorption, grading, and multiplication avalanche photodiode multiplication indicate that at high gains the excess noise factors approach values predicted by the conventional continuum theory. However, at lower gains the noise is suppressed. This is probably an artifact of the very thin multiplication layers which have been used to increase the gain-bandwidth product. From the frequency response of the noise power, a gain-bandwidth product of 60 GHz, which is consistent with the value of 57 GHz obtained directly from bandwidth measurements, is deduced     

Design considerations for high performance avalanche photodiodemultiplication layers

We have studied the effect of the thickness of the multiplication region on the noise performance characteristics of avalanche photodiodes (APD's). Our simulation results are based on a full band Monte Carlo model with anisotropic threshold energies for impact ionization. Simulation results suggest that the well known McIntyre expression for the excess noise factor is not directly applicable for devices with a very thin multiplication region. Since the number of ionization events is drastically reduced when the multiplication layer is very thin, the “ionization coefficient” is not a good physical parameter to characterize the process. Instead “effective quantum yield,” which is a measure of the total electron-hole pair generation in the device, is a more appropriate parameter to consider. We also show that for the device structure considered here, modeling the excess noise factor using a “discrete Bernoulli trial” model as opposed to the conventional “continuum theory” produces closer agreement to experimental measurements. Our results reinforce the understanding that impact ionization is a strong function of carrier energy and the use of simplified field-dependent models to characterize this high energy process fails to accurately model this phenomenon