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Phone: 334 727 8994, Fax: 334 724 4806.Current-voltage (I-V) characteristics and electroluminescence spectra of several ultraviolet and blue light-emitting 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-V plots indicated that, I / V x . These changes in the slope were interpreted as single-carrier space-charge-limited (SCL) transport across the diode active region. As bias increased the deep states were filled and for the 400-and 468-nm 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 430-nm 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 conduction-band edge and deep states, identified from the I-V characteristics, 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.

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A recombination lifetime of approximately 25 ns was extracted from measured reverse recovery storage times in AlGaN/GaN/AlGaN double heterojunction blue light emitting diodes. This experimentally determined lifetime is expected to arise from a combination of radiative and non-radiative processes occurring in the diodes. The non-radiative processes are likely to be due the presence of a high concentration deep-states as identified from the current-voltage and capacitance-voltage measurements. Current-voltage characteristics of these diodes were highly non-ideal as indicated by high values of the ideality factor ranging from 3.0 -7.0. Logarithmic plots of the forward characteristics indicated a space-charge-limited-current (SCLC) conduction in presence of a high density of "deep-level states" in the active region of the diodes. An analysis of these characteristics yielded an approximate density of these deep-level states as 2 x 10 17 /cm 3 . The density of deep-states extracted from capacitance-voltage measurements were in good agreement with that obtained from current-voltage measurements.