Shuzo Kagawa

Ionization rates for electrons and holes in GaAs

Ionization rates in GaAs are determined from the measurement of photocarrier multiplication. Pure electron and hole initiations are achieved by using the novel crater mesa structure and appropriate optical‐injection wavelengths. The ionization rates for holes are greater than that for electrons except at highest fields. This agrees with the studies of Stillman et al., except for the individual values. The ionization rates for electrons and holes are expressed as α=5.6×106 exp(−2.41×106/E) and β=1.5×106 exp(−1.57×106/E), respectively.

Crystal orientation dependence of ionization rates in germanium

Ionization rates in 〈111〉 and 〈100〉 germanium are determined experimentally. The ionization rates obtained are expressed as α=2.72×106 exp(−1.1×106/E), β=1.72×106 exp(−9.37×105/E) for 〈111〉 and α=8.04×106 exp(−1.4×106/E), β=6.39×106 exp(−1.27×106 /E) cm−1 for 〈100〉 where α and β are ionization rates for electrons and holes, respectively, and E is the electric field. Hole‐ to electron‐ionization‐rate ratios of 〈100〉 Ge are found to be greater than those of 〈111〉 Ge. The multiplication noise power of Ge avalanche photodiodes calculated by using the ionization rates obtained shows good agreement with experimental results.

Chemical Etching of Germanium with H3PO4?H2O2?H2O Solution

An H3PO4–H2O2–H2O solution is studied for possible use in the etching of germanium. The solution can be roughly classified into two ternary regions according to its etching characteristics: a (with a low H2O2 concentration) and b (with a high H2O2 concentration). Solutions in region b provide reproducible smooth and uniform surfaces. This solution can be used with SiO2 films and photoresists as a preferential etching mask material without dissolution or separation. It is suitable for processing germanium devices.

A low-noise n + np germanium avalanche photodiode

A low-noise n+np germanium avalanche photodiode which successfully operates in the wavelength region of0.8-1.5 \mum has been designed, fabricated, and tested. Low-excess noise factorF \sim 7is experimentally obtained at a multiplication factor ofM \sim 10and at a wavelength\lambda \sim 1.3 \mum, whereas the calculated one is 7.6. Quantum efficiency is as high as 80 percent and a cutoff frequency (-3 dB) is 500 MHz atM \sim 10and\lambda \sim 1.3 \mum. Overall performance of an n+np Ge-APD fabricated is estimated at\lambda = 1.3 \mum, and compared with that of a III-V alloy APD (InGaAs-InP) by calculating minimum detectable power. An n+np Ge-APD has shown minimum detectable power only 1.7 dB larger than that of a III-V APD at a signal-to-noise ratio of 22 dB and at a bandwidth of 100 MHz. An n+np Ge-APD also shows low-multiplication noise and considerably low minimum detectable power in the 0.8 μm region. Breakdown voltage of an n+np Ge-APD is 31 V and is much lower than that of a Si-APD. The n+np Ge-APD is found to be a useful detector in the whole wavelength region0.8-1.5 \mum of optical communication systems.

An n+‐n‐p germanium avalanche photodiode

Low‐noise germanium avalanche photodiodes of an n+‐n‐p structure have been investigated. Deep n+‐n‐p junctions have a lower noise than shallow n+‐p junctions because holes have a higher ionization coefficient in germanium, and these n+‐n‐p diodes have a higher hole‐to‐electron collection efficiency. An excess noise factor F≈7 at the multiplication factor of 10 are obtained at a wavelength of 1.3 μm, whereas F≈10 for n+‐p diodes. An internal quantum efficiency of 70–80% is obtained at 1.3 μm.

Fully ion‐implanted p+‐n germanium avalanche photodiodes

Germanium avalanche photodiodes with a shallow p+‐n junction have been fabricated using full ion implantation, together with a low temperature (650 °C), single‐stage annealing process. This procedure yielded high‐performance germanium avalanche photodiodes with a high rate of reproducibility. About 80% of the diodes obtained showed a dark current of 150–250 nA at 0.9 VB. At a multiplication factor of 10, low excess noise resulted (F≊6.5 at 1.55 mm and F = 8–9 at 1.3 mm), and deterioration of the response at 500 MHz was limited to 0.5–1 dB.

Wide-Wavelength InGaAs/InP PIN Photodiodes Sensitive from 0.7 to 1.6 µm

We have developed, for the first time, a wide-wavelength InGaAs/InP PIN photodiode for optical communication systems from 0.7- to 1.6-µm wavelength. The diode has a planar structure with an InP/InGaAs/InP double-hetero epitaxial wafer grown by chloride VPE. To obtain a highsensitivity to 0.7-µm wavelength light, we introduced a very thin InP cap layer (0.06 µm) and a shallow pn junction (0.27µm). Using this structure, we obtained a quantum efficiency of 76% for 0.78-µm light and 81% for 1.3-µm light. Dark current and capacitance are only 30 pA and 0.53 pF at 5 V. The frequency response is flat up to 1 GHz above 5 V at 0.78 µm.

Low noise avalanche photodiodes by channeling of 800‐keV boron into 〈110〉 silicon

Low noise avalanche photodiodes, which have an n+‐p‐π‐p+ structure, are reported. Channeled boron ions (800 keV) in the 〈110〉 of Si are used for forming the p layer. The characteristics of this diode are compared with those fabricated by 800‐keV random implantation. Low excess noise factors F=4–5 at a gain of 100 are obtained by using 〈110〉 channeled implantation, whereas F=6–7 for random implantation. By using parallel implantation, the uniformity of channeled distributions of boron ions are found to be fairly good at different locations in a wafer.

Wide-Wavelength InGaAs/InP PIN Photodiodes Sensitive From 0.7 To 1.55 um

We have demonstrated for the first time a wide-wavelength InGaAs/InP PIN photodiode for optical communication systems working area the 0.7 to 1.55 um wavelength region. The diode has a planar structure with InP/InGaAs/InP double-hetero epitaxial wafer grown by chloride VPE. To obtain high-sensitivity to 0.7 um wavelength light, it has a very thin InP cap layer (0.06 um) and a shallow p-n junction (0.27 um) is formed in the InGaAs layer. Quantum efficiencies for 0.78 um and 1.3 um wavelengths are 76% and 81%, respectively. Dark current and capacitance are as low as 30 pA and 0.53 pF at 5V. Frequency response is flat up to 1 GHz over 5V at 0.78 um.