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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.

Sputter-deposited Au, Pt, Cr, Ni and Cu contacts for n-type GaN films were studied using current-voltage (I -V ) and capacitance-voltage (C-V ) measurements. These films were grown by molecular beam epitaxy (MBE), heteroepitaxially on the basal plane of sapphire. The contacts were non-ideally rectifying in nature. Assuming that the non-ideality was due to effects of series resistance and recombination current, a computer curve fitting procedure was employed that enabled the separation of these effects from the thermionic emission current, thereby permitting the calculation of the barrier height. An analysis of the results indicates that the barrier heights for metal contacts on GaN are determined by the difference between the metal and the semiconductor electronegativities and substantially influenced by metal induced gap states (MIGS)/sputtering damage induced surface states (SDISS). The concentration of metal induced gap states/sputtering induced damage states was determined to be approximately 2.7 × 10 13 states cm −2 eV −1 .

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