Resonant-cavity light-emitting diodes (RCLED) are novel, high-efficiency light-emitting diodes which employ optical microcavities. These diodes have higher intensities and higher spectral purity as compared to conventional LED's, Analytical formulas are derived for the enhancement of the spontaneous emission along the optical axis of the cavity, The design rules for high-efficiency operation of RCLED's are established, The temperature dependence of the emission intensity is analyzed in the range 20-80 degrees and it is described by an exponential dependence with a characteristic temperature of 112 K. The modulation characteristics of RCLED's exhibit 3 dB frequencies of 580 MHz. Eye diagrams at transmission rates of 622 Mb/s are wide open indicating the suitability of RCLED's for high-speed data transmission.