We have theoretically investigated spatiotemporal current patterns and self-oscillating characteristics of negative-effective-mass (NEM) p(+)pp(+) diodes. Periodically oscillating current densities are presented as a gray density plot, showing rich patterns with the applied bias and doping concentration as controlling parameters. Such a pattern arises in the NEM p-base with a "N-shaped" velocity-field relation. Two-dimensional applied bias-doping concentration phase diagrams at different lattice temperatures are calculated in order to visualize the effect of lattice temperature on the self-oscillating regions. It is indicated that both the applied bias and the doping concentration strongly influence the patterns and self-oscillating frequencies, which are generally in the terahertz (THz) frequency band. The NEM p(+)pp(+) diode may therefore be used to develop a electrically tunable THz-frequency oscillator. (C) 2003 Elsevier Ltd. All rights reserved.