Abstract: A solid state infrared source is disclosed which is capable of modulation of the intensity of broadband infrared radiation. A silicon semiconductor body is provided with doped regions which have high emissivity for infrared and an intrinsic region which has low emissivity and low absorption for the infrared. The device is heated and maintained at a temperature of about 500.degree.K to effect the infrared radiation from the doped regions. Modulation is effected by controlling the presence of carriers in the intrinsic region, so as to modify the broadband infrared radiation. The modulating carriers may be due to optical modulation or they may be injected electrically. In either case, the heating may be effected by an external device or the doped regions may also provide a heating PIN diode structure which is forward biased in controlled fashion to attain the desired temperature.