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We report a normal incident Ge/Si avalanche photodiode by selective epitaxial growth. By eliminating germanium impact-ionization at high gain, high responsivity of 12A/W and large gain-bandwidth product of 310GHz have been achieved at 1550nm.

We report the first demonstration of a waveguide-integrated avalanche photodetector using Group-IV heterostructure materials. Such device achieved a responsivity of ∼0.8A/W at unity gain and an impressive gain-bandwidth product of ∼105GHz at 1550nm photon wavelength.

A separate-absorption-charge-multiplication Ge/Si avalanche photodiode with very high gain-bandwidth-product over 800GHz is reported. The origin of this dramatically high value is explained using well consentient measurement and simulation results.

The nonlinearity of a 300 GHz gain bandwidth Separate Absorption Charge Multiplication (SACM) Ge/Si avalanche photodiode was examined experimentally for varying multiplication factors. The maximum second order dynamic range was 84.8 dB⋅Hz½. The largest third order dynamic range was 101.5 dB⋅Hz⅔.

Travelling-wave GaInNAs-SOA was realized for the first time. The peak chip gain of 14dB and 3-dB gain bandwidth of 49 nm were obtained. The Gain dependence of the GaInNAs-SOA on temperature was much smaller than that of the conventional InP-based-SOA.

An avalanche photodiode (APD) with both an ultra-wide bandwidth and a high quantum efficiency is attractive for use in compact, highly-sensitive photoreceivers in optical communication systems at a wavelength of 1.55 μm. APDs with superlattice (SL) avalanche multiplication structures [1, 2, 3] are advantageous for obtaining a large gain-bandwidth (GB) product because their SL multiplication layers have high ionization-rate ratios. However, it is difficult to obtain a wide bandwidth above 20 GHz, while keeping a high quantum efficiency in conventional top- or back-illuminated SL-APDs [11] because there is a tradeoff between the quantum efficiency and the 3dB bandwidth which is limited by the carrier-transit time. On the other hand, in a photodiode with a waveguide (WG) structure, the quantum efficiency is independent of the bandwidth because the incident light and photogenerated carriers travel in different directions [4].

Semiconductor-laser amplifiers (SLA’s) can perform many optical-signal-processing functions. In addition to loss compensation and switching, a SLA can simultaneously amplify and detect an optical signal.1 Recently, two-contact amplifiers have demonstrated improved detection responsivi ty.23 Here, we show that a three-section SLA can further be used to monitor amplifier gain.

Recently, superlattice avalanche photodiodes (SL-APD’s)1,2 have been intensively investigated for high-sensitivity 10-Gbit/s long-wavelength optical communication systems.3-5 However, there have been few reports about SL-APD’s having both gain-bandwidth (GB) products larger than 100 GHz and submicroampere dark-current characteristics. This paper reports InAlAs/lnAlGaAs quaternary-well SL-APD’s satisfying both characteristics.

Even for lightwave transmission systems above 10 Gbit/s, highly sensitive and compact photoreceivers are preferable. An avalanche photodiode (APD) with a large gain-bandwidth (GB) product would be one of the most promising candidates for receivers in systems with such extremely high bit rates, as well as in systems with lower bit rates.1 Recently, we reported a superlattice (SL) APD with a GB product of 80 GHz under a 3-dB bandwidth of 12 GHz,2 where the SL allowed us to enhance the ionization-rate ratio for achieving the high GB product.3 To improve the GB product further, it is necessary to reduce the SL multiplication-layer thickness4 by overcoming the problem of the accompanying tunneling breakdown with thinning of the SL layer thickness. Here, we demonstrate an InAlAs/InGaAs SL-APD with a GB product of 130 GHz under a 3-dB bandwidth of 12 GHz by introducing a novel SL structure of less than 0.2-µm thickness.

Inherent in conventional separate absorption, grading and multiplication (SAGM) InP-based avalanche photodiode (APD) structures is a constraint between the doping level and length of the multiplication region.1-3 The thinner the multiplication region, the higher the doping level and the achievable gain-bandwidth product (GBW) of the device. Unfortunately, as the multiplication region becomes thinner, the device fabrication tolerances become very stringent, requiring p-diffusion junction depth control of ±200 A for a doping level of 6 × 1016 (Ref. 1). Even if the device can be fabricated, beyond a certain doping level [2 × 1017 cm−3 (Ref. 2)], the leakage current from tunneling in the InP multiplication region places a fundamental upper limit on the achievable GBW, which has been recently estimated to be 140 GHz.2 The highest GBW in an InP-based SAGM APD reported to date is 90 GHz,1 and Imai and Kaneda have commented that a GBW of 100 Gllz is unlikely to be achieved with a SAGM APD.3

(Invited) Highly sensitive photoreceivers are strongly needed for application to the higher bit rate optical communication systems around 10 Gb/s. To achieve high-sensitivity and high-speed responses in this high bit rate region, reduction of the photodetedor capacitance as well as widening of the bandwidth is crucial. Flip-chip bonding will be the key assembly technologyl2 to achieve these requirements, because surplus bonding pad area capacitance in conventional front-illuminated pho-todiodeand parasiticreactances associated with the interconnection can be minimized. In addition, hybrid assembly enables the best transistor choice for the following amplifier. This paper reports, to the best of our knowledge, the first implementation of the flip-chip, planar junction InGaAs avalanche photodiodes (APDs) with an ultra-low capacitance and a large gain-bandwidth product.

Large gain-bandwidth product and low-noise avalanche photodiodes (APDs) in the long-wavelength region are required in long-haul gigabit-rate lightwave systems. We have reported a practical device structure for planar GaInAs APDs with a successful guard ring effect in buried structure APDs.1 To obtain a large gain-bandwidth product, a higher carrier concentration n-InP multiplication layer must be employed to reduce avalanche buildup time. However, this results in deterioration of the excess noise factor for GaInAs APDs. We describe a design condition for achieving a large gain-bandwidth product and low-noise performance at the same time for GaInAs buried structure APDs grown by liquid phase epitaxy (LPE).

Previously we reported on the pulse1 and frequency response2 of InP/InGaAsP/InGaAs avalanche photodiodes with separate absorption, grading, and multiplication regions (SAGM-APD). In this paper we describe several modifications we have made to the device structure, shown schematically in Fig. 1, to achieve significant improvement in both the frequency and pulse response. The changes include (1) reduction of the total depletion width to decrease the transit time of the free carriers, (2) use of low-resistance substrates to reduce the RC time constant, (3) introduction of an additional transition layer to eliminate effectively hole trapping at the heterojunction interfaces, and (4) increasing the carrier concentration in the multiplication region to reduce avalanche buildup time.