A laser diode for producing an optical beam in a direction substantially perpendicular to epitaxial layers, comprising:
- a substrate having an upper major surface and a lower major surface, said substrate comprising a single crystal of a first semiconductor material having a first conductivity tape, said substrate being surrounded by a first side wall with a first lateral size;
- an active layer having an upper major surface and a lower major surface and provided on said upper major surface of said substrate epitaxially, said active layer being surrounded by said second side wall and having a second lateral size that is substantially smaller than said first lateral size, and active layer comprising an undoped single crystal of a second semiconductor material different from said first semiconductor material and producing an optical beam by a stimulated emission, said active layer having a first refractive index;
- a contact layer having an upper major surface and a lower major surface and provided on said upper major surface of said active layer epitaxially, said contact layer being surrounded by a third side wall and having a third lateral size substantially smaller than said first lateral size, said contact layer comprising a third semiconductor material different from said second semiconductor material and doped to said first conductivity type, said contact layer having a second refractive index;
- optical confinement means providing on said upper major surface of said substrate in contact with said second and third side walls for confining said optical beam in said active layer and in said contact layer, said optical confinement means comprising a material that has a third refractive index that is smaller than any of said first and second refractive indices;
- a convex mirror part provided on said lower major surface on said substrate to protrude outward from said substrate in a direction substantially perpendicular to said lower major surface of said substrate, said convex mirror part comprising a spherical surface for reflecting back said optical beam and concentrating the same in said active layer;
- a second mirror part provided in correspondence to said upper major surface of said contact layer for reflecting back said optical beam to said active layer;
- first electrode means provided on said upper major surface of said contact layer for injecting carriers of a first polarity;
- second electrode means provided on said lower major surface of said substrate for injecting carriers of a second, opposite polarity;
- and
- optical passage means provided at least on one of said spherical surface of said convex lens part and said upper major surface of said contact layer for emitting said optical beam,
- said convex mirror part and said second mirror part being arranged in opposing relationship, said substrate, said active layer and said contact layer being interposed between said mirror parts so as to present a resonant cavity.