| 摘要 |
PURPOSE:To make it possible to neglect a tunnel current to be a dark current, by properly enlarging a minimum distance between a P-N junction in a guard ring and a heterojunction facing thereto. CONSTITUTION:An N type compound semiconductor layer 2 having a relatively small band gap and an N type compound semiconductor layer 4 having a relatively large band gap are formed on an N<+> type compound semiconductor substrate. On the other hand, a P<+> type semiconductor region 5 is formed on the surface side of the layer 4, and a P<+> type semiconductor region 7 is formed around the region 5, deeper than the same. A heterojunction 3 is so formed that a minimum distance Lb between a heterojunction 3b and a P-N junction 8 is larger than a distance La-Lc or substraction of a depth Lc between both ends of the junction 6 and the region 7 from a minimum distance La between a heteojunction 3a and the P-N junction 8. Thus, even if a bias voltage high enough to reach just below an avalanche voltage of a diode is applied to the junctions 6 and 8, a dark current as a result of a tunnel current can be neglected. |
