Effect of deeplevel states on current–voltage characteristics and electroluminescence of blue and UV lightemitting diodes

Current–voltage I–V characteristics and electroluminescence spectra of several ultraviolet and blue lightemitting diodes LEDs emitting nominally at 380, 400, 430, and 468 nm were studied. These diodes exhibited an Ohmic regime at low forward biases; then the current increased sharply as bias increased. Several changes in the slope of logarithmic I–Vplots indicated that, I ∝ Vx. These changes in the slope were interpreted as singlecarrier spacechargelimited SCL transport across the diode active region. As bias increased the deep states were filled and for the 400 and 468nm diodes ideality factors of ∼2 were obtained. This indicated that, as bias increased the transport mechanism changed from SCL conduction to recombination of injected carriers in the spacecharge region. For the 380 and 430nm diodes, ideality factors >>2 were obtained, although the observed electroluminescence spectrum indicated substantial radiative recombination. For the diode emitting at 430 nm, several peaks including the major peak at ∼424 nm appeared to have resulted from transitions between the conductionband edge and deep states, identified from the I–Vcharacteristics, likely to be associated with Zn doping of the InGaN active region. Deep states in the other diodes appeared to be ineffective in the radiative recombination process.