| 摘要 |
PURPOSE:To improve the frequency characteristic and optical responsiveness of a voltage by providing a buffer layer in which a minute amount of P-type impurity concentration is continuously varied between second and third semiconductors. CONSTITUTION:In order to improve optical responsiveness when a voltage is applied to an element, it is necessary that electrons and holes do not retain at a part to become a barrier of an energy band diagram and do not recombine. Thus, the width of a transition region between an N-type layer and an I-type layer is broadened, and the barrier is smoothly varied. Actually, a layer in which an impurity concentration is gradually varied in a boundary between N and I, i.e., Fermi level is continuously varied is formed. That is, a band gap of a boundary between I and N of second and third semiconductors is continuously varied. Thus, electrons and holes are rapidly moved upon voltage slope, the recombination of the electrons and the holes does not occur, and an element having excellent optical responsiveness and voltage frequency characteristics can be manufactured.
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