Field-effect transistor, bipolar transistor, and methods of fabricating the same

A bipolar transistor comprising:

• a collector layer disposed above a substrate;
• a base layer disposed on the collector layer;
• a first semiconductor layer disposed above the base layer and a base electrode disposed in spaced relation to the first semiconductor layer;
• a second semiconductor layer disposed on the first semiconductor layer to protrude from side surfaces of the first semiconductor layer;
• and
• an emitter electrode disposed on the second semiconductor layer,
• wherein the first semiconductor layer consists of gallium arsenide and the second semiconductor layer comprises indium gallium arsenide.

A bipolar transistor comprising:

• a collector layer disposed above a substrate;
• a base layer disposed on the collector layer;
• a first semiconductor layer disposed above the base layer and a base electrode disposed in spaced relation to the first semiconductor layer;
• a second semiconductor layer disposed on the first semiconductor layer to protrude from side surfaces of the first semiconductor layer;
• and
• an emitter electrode on the second semiconductor layer,
• wherein the emitter electrode is composed of a multilayer structure including a plurality of metal layers, of which the metal layer closer to the substrate contains titanium.

A field-effect transistor comprising:

• a substrate having a channel layer;
• first semiconductor layers disposed in at least two regions located above the channel layer and spaced apart in a direction parallel to a substrate surface;
• second semiconductor layers disposed on the respective first semiconductor layers to protrude from respective side surfaces of the first semiconductor layers;
• ohmic electrodes disposed on the respective second semiconductor layers;
• and
• a gate electrode disposed in a region located above the channel region and lying between the first semiconductor layers in spaced relation to the side surfaces of the first semiconductor layers;
• wherein each of the first semiconductor layers is composed of gallium arsenide and each of the second semiconductor layers is composed of indium gallium arsenide.

A field-effect transistor comprising:

• a substrate having a channel layer;
• first semiconductor layers disposed in at least two regions located above the channel layer and spaced apart in a direction parallel to a substrate surface;
• second semiconductor layers disposed on the respective first semiconductor layers to protrude from respective side surfaces of the first semiconductor layers;
• ohmic electrodes disposed on the respective second semiconductor layers;
• and
• a gate electrode disposed in a region located above the channel region and lying between the first semiconductor layers in spaced relation to the side surfaces of the first semiconductor layers;
• wherein each of the ohmic electrodes is composed of a multilayer structure including a plurality of metal layers, of which the metal layer closer to the substrate contains titanium.

A bipolar transistor comprising:

• a collector layer disposed above a substrate;
• a base layer disposed on the collector layer;
• a first semiconductor layer disposed above the base layer and a base electrode disposed in spaced relation to the first semiconductor layer;
• a second semiconductor layer disposed on the first semiconductor layer to protrude step-like from side surfaces of the first semiconductor layer;
• and
• an emitter electrode disposed on the second semiconductor layer, an area where the emitter electrode faces the second semiconductor layer is substantially equal to an area of the second semiconductor layer,
• wherein the first semiconductor layer comprises gallium arsenide and the second semiconductor layer comprises indium gallium arsenide;
• wherein the first and second semiconductor layers are comprised of different materials.