Abstract: A field-effect transistor has a composite channel structure having a first channel layer containing GaInP semiconductor and a second channel layer containing GaAs semiconductor. When the electric field is low in the channel, a channel current is primarily conducted in the second channel layer. When the electric field is high, the electrons flowing in the second channel layer move through real space transition to the first channel layer. These electrons conduct in the channel primarily in the first channel layer. Since GaInP semiconductor has a wider forbidden bandwidth than that of GaAs semiconductor, the avalanche breakdown voltage of GaInP semiconductor is higher than that of GaAs semiconductor. When the electric field is high, the conduction electrons travel in this GaInP semiconductor layer. This also improves the avalanche breakdown voltage of the field-effect transistor.

Abstract: The present invention relates to a field-effect transistor which is improved such that the linearity of mutual conductance gm is flattened over a wider range of gate bias. This field-effect transistor is a MESFET comprising a channel layer and a cap layer in Schottky-contact with a gate electrode. In particular, between the channel layer and the cap layer, one or more auxiliary layers having a doping concentration lower than that of the channel layer and higher than that of the cap layer are provided. The doping concentration of one or more auxiliary layers is set such that the doping profile of a laminated structure constituted by the channel layer, one or more auxiliary layers, and cap layer exponentially lowers from the channel layer toward the cap layer. According to this configuration, the depletion layer can effectively be controlled over a wider range of gate bias, the long gate effect and the like are suppressed, and the linearity of mutual conductance gm is improved.

Abstract: It is an object of the present invention to provide a highly reliable optical module circuit board having a sufficient mechanical strength with respect to an external stress.

Abstract: It is an object of the present invention to provide an optical module having a structure in which alignment precision of sleeves to be accommodated to a housing can be improved with a simple operation. The optical module according to the present invention is characterized by providing special structures for defining the positions of the sleeves to a sleeve holder for holding the sleeves, and the housing having a cavity for accommodating the sleeves. In particular, the housing includes support portions each having a reference surface for defining the fixing position of the corresponding sleeve. The sleeve holder includes spring pieces each for urging the sleeve to the reference surface.