Indium phosphide Gunn diode with dopant gradient

A Gunn diode, comprising:

• an n-type active layer made of an InP semiconductor body;
• two n.sup.+ -type layers sandwiching the n-type active layer, each of which is having a donor concentration greater than the n-type active layer and connected with a metallic electrode;
• wherein the donor impurity concentration in the n-type active layer is graded along a direction perpendicular to a contact plane between the n-type active layer and the n.sup.+ -type layers, and an average concentration gradient G of the donor impurity concentration in the n-type active layer simultaneously satisfies the following three inequalities:
• G>(A.sub.1 N/L)exp(-NL/S.sub.3)
• G<(A.sub.3 N/L)exp(-NL/S.sub.4)
• G<2N/L
• where L is a thickness of the n-type active layer, N is an average concentration of the donor impurity in the n-type active layer, S.sub.3 =1.2.times.10.sup.12 cm.sup.-2 is a constant, S.sub.4 =4.0.times.10.sup.12 cm.sup.-2 is a constant, A.sub.1 =2.0 is a constant, and A.sub.3 =3.4 is a constant;
• and
• the n-type active layer has a thickness L not greater than 1.5 .mu.m, while the product NL of the thickness L of the n-type active layer and the average concentration N of the donor impurity is not greater than 2.0.times.10.sup.12 cm.sup.-2.