Abstract: An optical semiconductor device includes a lower electrode layer formed over a semiconductor substrate, an infrared absorption layer formed over the lower electrode layer 26, and an upper electrode layer 38 formed over the infrared absorption layer 36. The infrared absorption layer includes a quantum dot having dimensions different among directions stacked, and is sensitive to infrared radiation of wavelengths different corresponding to polarization directions.

Abstract: An infrared photodetector including a layer structure of an intermediate layer, and a quantum dot layer having a narrower band gap than the intermediate layer and including a plurality of quantum dots alternately stacked, and detecting photocurrent generated when infrared radiation is applied to the layer structure to thereby detect the infrared radiation, the infrared photodetector further including a first barrier layer provided on one side of the quantum dot layer and having a larger band gap than the intermediate layer; and a second barrier layer provided on the other side of the quantum dot layer and having a larger band gap than the intermediate layer.

Abstract: A quantum dot infrared photodetector includes a quantum dot structure including intermediate layers, and a quantum dot layer sandwiched between the intermediate layers and including quantum dots whose energy potential is low for carriers, the intermediate layers and the quantum dots being formed of a III-V compound semiconductor with the V element being As, and an AlAs layer being provided on one of the interfaces between the intermediate layers and the quantum dot layer including the quantum dots and covering at least the quantum dots.

Abstract: An optical semiconductor device includes a lower electrode layer formed over a semiconductor substrate, an infrared absorption layer formed over the lower electrode layer 26, and an upper electrode layer 38 formed over the infrared absorption layer 36. The infrared absorption layer includes a quantum dot having dimensions different among directions stacked, and is sensitive to infrared radiation of wavelengths different corresponding to polarization directions.

Abstract: An infrared photodetector including a layer structure of an intermediate layer, and a quantum dot layer having a narrower band gap than the intermediate layer and including a plurality of quantum dots alternately stacked, and detecting photocurrent generated when infrared radiation is applied to the layer structure to thereby detect the infrared radiation, the infrared photodetector further including a first barrier layer provided on one side of the quantum dot layer and having a larger band gap than the intermediate layer; and a second barrier layer provided on the other side of the quantum dot layer and having a larger band gap than the intermediate layer.

Abstract: In a method of manufacturing a thermal-type infrared sensor including a thermosensitive part, a bolometer material is formed as the thermosensitive part and is subjected to post-processing to control a temperature coefficient of resistance in the bolometer material. The bolometer material may be formed by titanium or vanadium.

Abstract: At a heat treatment temperature in a reducing atmosphere of Ar and H.sub.2, a precursory film of V.sub.2 O.sub.5 is reduced into a VO.sub.x film with the heat treatment temperature selected in a predetermined temperature range between 350 .degree. C. and 450.degree. C., both exclusive, to control a resistivity of the VO.sub.x film, where x is greater than 1.875 and less than 2.0. The VO.sub.x film is not susceptible to a metal-semiconductor phase transition inevitable in VO.sub.2 at about 70.degree. C. and is excellent for use in a bolometer-type infrared sensor. When reduced at 350.degree. C. and 450.degree. C. the resistivity and its temperature coefficient of the VO.sub.x film at room temperature are 0.5 and 0.002 .OMEGA. cm and -2.2% and 0.2% per degree Celsius.