Fujitsu Corporation

Takashi Mikawa

Takao Kaneda

Masahiro Kobayashi

Tetsuzo Yoshimura

Nami Yasuoka

Haruhiko Kuwatsuka

Kazuo Nakajima

Susumu Yamazaki

Shuichi Miura

Osamu Ibaragi

For example, a surface emitting semiconductor laser and a driver IC are arranged three-dimensionally to put a submounting substrate between them, and LSIs such as a CPU, etc. are mounted on the driver IC. The surface emitting semiconductor laser is formed of the epitaxial lift-off (ELO) process and has a thickness of about 10 &#x3bc;m. A through hole is provided to all the submounting substrate, the surface emitting semiconductor laser, the driver IC, and the LSIs. These parts are connected electrically mutually via conductor in the through hole.

Optical interconnection apparatus and interconnection module

An APD includes a substrate formed of n.sup.+ -type Al.sub.x Ga.sub.1-x Sb or Al.sub.x Ga.sub.1-x Sb.sub.y As.sub.1-y semiconductor, whose aluminum content ratio x is typically within a range from 0.1 to 0.3. A light absorbing layer is formed of an-type GaSb semiconductor on the substrate. An avalanche multiplication layer is formed of n-type Al.sub.x Ga.sub.1-x Sb or Al.sub.x Ga.sub.1-x Sb.sub.y As.sub.1-y semiconduct, whose aluminum content ratio x is from 0.02 to 0.1, typically 0.065, so that an ionization rate ratio of positive and negative carriers is essentially maximized by a resonant impact ionization phenomenon. A p.sup.+ -region is formed as a surface layer of n-type Al.sub.x Ga.sub.1-x Sb or Al.sub.x Ga.sub.1-x Sb.sub.y As.sub.1-y semiconductor on the avalanche multiplication layer or directly in the avalanche multiplication layer so as to form a pn junction. Electrodes are formed on the p-type region and the substrate so as to apply a bias voltage to the APD. A light to be detected is injected through the substrate via an opening in the substrate electrode, while producing no carriers therein, into the light absorbing layer. The avalanche multiplication layer generates resonant impact ionization with only the positive carriers from the light absorbing layer, so that low noise and fast operation of the APD is achieved. Furthermore, the APD structure of the invention allows for easy design of an APD.

Semiconductor photodiode

An APD of the invention has its avalanche multiplication layer, made of a material which can cause a resonant impact ionization therein, between its window layer having a big band gap energy and light-absorbing layer having a band gap energy smaller than the window layer. The layout of the invention lowers field intensity in the light absorbing layer, thus, a dark current produced by a tunnel effect in the light absorbing layer is reduced. Because of great amount of ionization ratio in the resonant impact ionization phenomena, both excessive noise factor and the applied operating DC voltage to the APD can be much less than that of the prior art APD without employing the resonant impact ionization, as well as the operation speed can be increased. The reduced operation voltage protects unexpected local avalanche breakdown in the pn junction area, thus uniform and reliable avalanche multiplication is always initiated in the multiplication layer, resulting in reduction of dark current and allowing a voltage margin. For fabricating the APD, there is no difficult problem like the difficulty of doping n.sup.+ impurity in the p-type window layer in the prior art APD employing the resonant impact ionization. Excessive noise factor below 3, operation at 12.5 V, and operation at 10 GHZ are achieved.

Avalanche photodiode with uniform avalanche multiplication

A buried structure avalanche multiplication photodiode (APD) is provided with a surface level difference between the multiplication region and guard ring region. The APD has a so-called separated absorption and multiplication region structure comprising an n-InGaAs light absorbing layer and an n-InP multiplication layer. The surface level difference is provided by selective growth of the layer in which the guard ring is formed or selective removal of the layer over the multiplication region. In the APD, the pn junction is level throughout the multiplication region and guard ring region or is made farther apart from the light absorbing layer in the guard ring region than in the multiplication region, and a significant reduction of dark current due to tunneling current in the InGaAs layer and/or InGaAsP layer is obtained. Moreover, the breakdown voltage difference of the pn junction in the multiplication region and the guard ring region has also been increased.

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Tokyo, Japan

Takashi Mikawa