The present invention provides an applications-oriented nitride compound semiconductor substrate, and devices based on it, whose lattice constant can be tuned to closely match that of any nitride thin film or films deposited on it for specific electronic or optoelectronic device applications. Such application-oriented nitride substrates, which can be composed of ternary InxGa1-xN, AlyIn1-yN, AlzGa1-zN, or quaternary AlaInbGa1-a-bN alloy compounds, minimize lattice-mismatch-induced dislocations and defects between the epitaxial films and the substrate on which the device layers are grown, leading to substantially improved device performance.