Integration of GaAs vertical junction field effect transistor and photodiode using selective metalorganic chemical vapor deposion

Abstract

For the OEIC (Optoelectronic Integrated Circuit) the new receiver structure was proposed and fabricated which is consisted of the PIN photodiode and the VJFET (Vertical Junction Field Effect Transistor). In the fabrication the highly Zn-doped p-type gate layer raises the autodoping phenomeana in the atmospheric pressure MOCVD (Metalorganic Chemical Vapor Deposition). Thus the low doped n-type channel is disappeared in the second-step epitaxy. So that the carbon-doped p-type gate layer is used. In the second-step epitaxy the growth is selective using the silicon dioxide mask. In this case the growth thickness profile is very complex. But the grown volume has simple relation to the mask area for given mask material kinds. Thus it is modeled by simple method and gives accurate result when the mask size is what we use about 100 $\mu$m which is the order of the maximum migration length of growing source ont the wafer in MOCVD. The growth volume increase on GaAs surface is measured as 0.4 atimes the area of the silicon dioxide mask times the epi-thickness without mask. Also the fine gate pattern for the better operation the RIE (Reactive Ion Etching) of GaAs is used but this gives the damages to the etched surface and degraded the device characteristics. Also for the design of OEIC the optimum parameter ranges are discussed for the optical and the electrical devices. To maximize the photodiode operation the VJFET should operate in SIT mode so that the receiver operation should be maximized. But the model of VJFET in SIT mode of the proposed structure which includes the drain-to-gate region as well as the sourceto-gate region was not reported until now so that the analysis and analytic model for the SIT was needed. The results are shown compared with the results of the PISCES2B 2-dimensional device simulator. According to the comparison with the 2-dimensional device simulator, it is thought that the model shows good description of SIT.