PURPOSE: To enable a P-type gallium arsenide semiconductor doped with C to be offered by a method wherein a P-type GaAs semiconductor layer is formed through a vapor growth method accompanied by thermal decomposition reaction making organic metal having methyl groups, arsine, and alkyl compound of arsenic serve as sources respectively.

CONSTITUTION: A P-type GaAs layer 24, a lower clad layer 26, an active layer 28, an upper clad layer 30, and a contact layer 32 are all formed through an MOCVD method. When the P-type GaAs layer 24 is formed, organic metal having methyl groups such as trimethyl gallium (CH3)3Ga, arsine AsH3, and alkyl compound of arsenic such as trimethyl arsine (CH3)3As are used as material. In this case, the reaction concerned is expressed by a reaction formula, (CH3)3Ga+AsH3→GaAs+3CH4↑(CH3)3Ga+(CH3)3As→GaAs+4CH4↑+2C. By this setup, GaAs can be doped with carbon but can not be controlled in carbon concentration. Then, carbon concentration is controlled by adding arsine without changing a growth temperature. Thereafter, the lower clad layer 26, the active layer 28, and the upper clad layer 30 are formed using trimethyl aluminum, trimethyl gallium, arsine, and hydrogen selenide as material.