| 摘要 |
PROBLEM TO BE SOLVED: To provide a semiconductor device in which a varactor is monolithically formed on the same substrate together with a hetero device, and to provide its manufacturing method. SOLUTION: A GaAs buffer layer 12 constituting the active layer of a HEMT, channel layer 13, a spacer layer 14, an electron supply layer 15 and a barrier layer 16 are formed sequentially on a semiinsulating GaAs substrate 11. An N-type low-resistance layer 17c composed of GaAs or the like doped with Si and a concentration gradient layer 18a composed of GaAs or the like in which the concentration of doped Si is changed in the direction of a layer thickness are formed on the barrier layer 16 in a region in which the varactor is formed. A P-type low-resistance region 21 doped with Zn is formed on the surface of the layer 18a. As a result, the varactor which is constituted of the region 21 and the layer 17 interposing the layer 18a and in which a capacitance value can be changed freely by an applied external control signal is formed monolithically with the HEMT.
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