Optoelectronics is quickly becoming a fast emerging technology field. It refers to detect or emit electromagnetic radiation, and convert it into a form that can be read by an integrated measuring device. These devices can be a part of many applications like photodiodes, solar cells, light emitting diode (LED), telecommunications, medical equipment, and more. Due to their different applications, the semiconductor optoelectronic devices can be divided by their operating wavelength and working mechanisms. In this work, I have focused on semiconductor plasmonic systems operating in the mid-infrared and on the optical detectors made of 2D materials operating in the UV-visible spectral range. Mid-infrared plasmonic devices are very attractive for chemical sensing. Our results show that ultra-doped n-type GaAs is ideal for mid-infrared plasmonics, where the plasmon wavelength is controlled by electron concentration and can be as short as 4 μm. Ultra-doped n-type GaAs is achieved using ion implantation of chalcogenides like S and Te followed by nonequillibrium thermal annealing, namely ns-range pulsed laser melting or ms-range flash lamp annealing. I have shown that the maximum electron concentration in our GaAs layer can be as high as 7×10¹⁹ cm⁻³, which is a few times higher than that obtained by alternative techniques. In addition to plasmonic applications, the ultra-doped n-type GaAs shows negative magnetoresistance, making GaAs potential material for quantum devices and spintronic applications. UV-visible optical detectors are made of 2D materials based on van der Waals heterostructures, i.e. transition metal dichalcogenides (TMDCs) e.g. MoSe₂ and transition metal chalcogenophosphates (TMCPs) with a general formula MPX₃ where M=Fe, Ni, Mn and X=S, Se, Te. The external quantum efficiency of a self-driven broadband photodetector made of a few layers of MoSe₂/FePS₃ van der Waals heterojunctions is as high as 12 % at 532 nm. Moreover, it is shown that multilayer MoSe₂ on FePS₃ forms a type-II band alignment, while monolayer MoSe₂ on FePS₃ forms a type-I heterojunction. Due to the type-I band alignment, the PL emission from the monolayer MoSe₂ is strongly enhanced.