Fujitsu Corporation

Takao Kaneda

Kazuo Nakajima

Takashi Mikawa

Masahiro Kobayashi

Susumu Yamazaki

Tatsunori Shirai

Shuzo Kagawa

Yasuo Baba

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 semiconductor device for receiving light includes a first semiconductor layer having a first conductivity type; the device further includes a second semiconductor layer having the first conductivity type, contacting the first semiconductor layer, having a forbidden bandwidth larger than that of the first semiconductor layer and distributed so that the forbidden bandwidth has a maximum value at an intermediate position in the vertical direction and of the second semiconductor layer. The semiconductor device further includes a third semiconductor region having a second conductivity type opposite the first conductivity type, contacting the second semiconductor layer and having a forbidden bandwidth smaller than that of the third contact end portion between the semiconductor region and the second semiconductor layer and larger than that of the first semiconductor layer. The third semiconductor region having the second conductivity type acts as a window layer through which incident light is transmitted.

Semiconductor device for receiving light

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.

Avalanche multiplication photodiode having a buried structure

A semiconductor device, and a method for manufacturing it in which ions of beryllium are implanted into a germanium substrate to form a layer containing p-type impurity material. There after the substrate is heated at a temperature in the range of 400.degree. C. to 700.degree. C. to diffuse the beryllium ions into the substrate so that the concentration of beryllium at the surface of the impurity layer is in the order of 10.sup.17 cm.sup.-3 or more. In one embodiment, a p-type channel stopper is formed locally in a p-type germanium substrate and an n-type active layer is formed in a region surrounded by, and isolated from, the channel stopper region. In another embodiment, a relatively shallow p-type active layer is formed at one part of an n-type germanium substrate and p-type guard ring regions are formed surrounding, and partly overlapping said p-type active layer. In a further embodiment, a p-type island region is formed at one part of an n-type germanium substrate, and an n-type region is formed within said p-type region. In these embodiments, the p-type channel stopper region, p-type guard ring regions and the p-type island region are all formed by implanting ions of beryllium into the germanium substrate.

Growing community of inventors

Kawasaki, Japan

Takao Kaneda