Hiroshi Kanbe

New InGaAs/InP avalanche photodiode structure for the 1-1.6 µm wavelength region

Low dark current and low multiplication noise properties for an In 0.53 Ga 0.47 As/InP avalanche photodiode are described. The diode is prepared with an In 0.53 Ga 0.47 As light absorption layer and an InP avalanche multiplication region. The lowest dark current density of 5.2 \times 10^{-4} A/cm2is obtained at 90 percent of a breakdown voltage. Multiplication noise power is proportional to the 2.7th power of the current multiplication factor. Impact ionization coefficient by holes is larger by 2-3 times than that by electrons in

Tunneling Current in InGaAs and Optimum Design for InGaAs/InP Avalanche Photodiode

Breakdown voltage and dark current density in p+n and n+p In0.53Ga0.47As diodes are compared with theoretical values taking the backward tunneling current into account. Predominant origin of dark current in an InGaAs diode is attributed to the tunneling current. Using these results, optimum design of an InGaAs/InP avalanche photodiode (APD) to obtain low dark current, high multiplication gain, high quantum efficiency and fast response is also discussed.

Characteristics in InGaAs/InP avalanche photodiodes with separated absorption and multiplication regions

Improved characteristics of compound semiconductor avalanche photodiodes with separated absorption and multiplication regions (SAM) are discussed. Temperature dependences of dark current and breakdown voltage show that the tunneling current in the narrow energy gap layer can be suppressed in InGaAs/InP APDs with the SAM structure. Dark currents above punch-through voltages, at which the depletion layer reaches the InP-InGaAs heterointerface, are caused by the generation-recombination process in the InGaAs and at the heterointerface. Dark currents near breakdown depend on the n-layer thickness and are strongly affected by the electric field strength in the ternary layer. Tunneling currents are dominant in diodes with thin n-InP layers, while the generation-recombination processes in the InGaAs layers are dominant in those with a thick n-InP layer. The dark current was as low as7.8 \times 10^{4}A/cm2atM = 10when the interface electric field strength is reduced. A maximum multiplication factor of 60 was observed for the6 \times 10^{-7}A initial photocurrent. Rise time and full width at half maximum in a pulse response waveform were 100 and 136 ps, respectively, atM = 10.

Nanometer‐scale imaging of potential profiles in optically excited n‐i‐p‐i heterostructure using Kelvin probe force microscopy

We report on measurements of the potential profile of a GaAs/AlGaAs n‐i‐p‐i multiple quantum well structure using a scanning Kelvin probe force microscope (KFM). Using this novel technique we directly measure with meV precision and sub‐100 nm spatial resolution the potential difference between n‐i‐p‐i layers with and without external optical excitation. The measured potential profiles, which have not been directly imaged previously, agree well with potential profiles calculated for optically excited n‐i‐p‐i structures, but modified by band bending effects at the surface.

Nonlinear absorption in n-i-p-i-MQW structures

Absorptive nonlinearity in a GaAs/AlGaAs n-i-p-i-MQW (multiple quantum well) structure consisting of alternating n-AlGaAs, i-GaAs/AlGaAs MQW, and p-AlGaAs layers is investigated. A change in the absorption coefficient of more than 4000/cm is obtained in the i-MQW layer with an extremely low excitation intensity on the order of 1 mW/cm/sup 2/. The figure of merit for absorptive nonlinearity, sigma /sub ch/, defined as the change in the absorption coefficient induced by excitation of an electron-hole pair per unit volume, is experimentally evaluated to be 7*10/sup -13/ cm/sup 2/, which is an order of magnitude larger than that for saturation of excitonic absorption in a conventional MQW structure. This experimental value agrees well with the theoretical estimation, which is calculated assuming an optical nonlinear process. >

InGaAs/InP separated absorption and multiplication regions avalanche photodiode using liquid- and vapor-phase epitaxies

Heterostructure planar InGaAs/InP avalanche photodiodes, which consist of a vapor-phase epitaxial InP avalanche multiplying layer and a liquid-phase epitaxial In 0.53 Ga 0.47 As optical absorption layer, were fabricated. Dark current, multiplication, spectral response, and pulse response characteristics are reported. Diodes were prepared by InGaAs liquid-phase epitaxy on an InP substrate, followed by InP vapor-phase epitaxy. The vapor-phase epitaxy was adopted in the InP growth to avoid ternary layer melting encountered in the liquid-phase process. Cd diffusion was carried out in the InP layer to form a p-n junction. A uniform multiplication factor of 5.5 was observed without a guard ring. The quantum efficiency was 70 percent in the 1-1.6 \mu m wavelength region without antireflection coating. Dark current density was as low as 1.5 \times 10^{-4} A/cm2at 90 percent of breakdown voltage. A fast rise time of 100 ps was observed.

Silicon avalanche photodiodes with low multiplication noise and high-speed response

Low-noise and high-speed silicon avalanche photodiodes with low breakdown voltage are reported. The diode structure with a low-high-low impurity density profile is proposed to have low-noise characteristics. Multiplication noise and depletion layer width of several structures are compared theoretically, and effects of impurity density profile of the avalanche region are discussed. Built-in field is also provided to realize high-speed response without increasing operating voltage. Silicon avalanche photodiodes with the above mentioned structure have been fabricated with long time substrate annealing, ion implantation, and epitaxial growth. Attained performances are as follows: noise parameter k = 0.027 - 0.040, output pulse half width τ = 260 ps for a mode-locked Nd:YAG laser pulse, gain-bandwidth product up to 300 GHz at M = 400, quantum efficiency 0.55 - 0.66 at the 0.81- to 0.83-µm wavelength, and breakdown voltage about 100 V.

Band‐edge optical absorption spectra of GaAs quantum wires calculated by multiband effective mass theory

Optical absorption spectra of quasi‐1D GaAs quantum well wires are theoretically investigated within the framework of multiband effective mass theory. In the calculation, the mixing of heavy‐hole and light‐hole bands resulting from both 1D quantum confinement and electron‐hole Coulomb interaction is considered. Detailed excitonic structures in the absorption spectrum near the band edge are clarified by taking into account Coulombic bound states and unbound continuum states. Polarization dependence of the optical absorption spectra is discussed in terms of the band mixing effects.

Low-temperature Zn- and Cd-diffusion profiles in InP and formation of guard ring in InP avalanche photodiodes

Zn and Cd diffusion in InP were studied in the wide temperature range of 350-580°C to realize a guard ring in InP avalanche photodiodes (APDs). Hole-concentration profiles for Zn and Cd diffusions at various temperatures were found to be expressed by a unified empirical curve, which decreases exponentially with the distance from the surface, and abruptly decreases at the diffusion front. A graded junction can be formed by diffusion at temperatures lower than 500°C for the n-InP background carrier concentration of 1016cm-3, while an abrupt junction can be formed by higher temperature diffusion. Breakdown voltages for the graded-junction diodes formed by low-temperature diffusion were confirmed to be higher than those for the abrupt-junction diodes formed by the higher temperature diffusion. A guard ring formed by the low-temperature Cd diffusion enabled planar-type InP and InGaAs/InP APDs to have uniform multiplication in the photosensitive area without any edge breakdown.

Improved germanium avalanche photodiodes

New kinds of germanium avalanche photodiodes with n+-n-p and p+-n structures were devised for improved excess noise and high quantum efficiency performance. Multiplication noise, quantum efficiency, and pulse response were studied and compared with those of the conventional n+-p structure diode. Multiplication noise of the new type of diodes were measured in the wavelength range between 0.63 and 1.52 μm. The effective ionization coefficient ratio of the p+-n diode was lower than unity at a wavelength longer than 1.1 μm and 0.6-0.7 at 1.52 μm, and that of the n+-n-p diode was 0.6-0.7 in the whole sensitive wavelength region. Response times were evaluated by using a mode-locked Nd:YAG laser beam and a frequency bandwidth wider than 1 GHz was estimated. Receiving optical power levels were compared with each other using parameters measured in this study.