Electrical Characterization of GaN Based Ultraviolet and Blue Light Emitting Diodes

摘要

Gallium nitride based ultraviolet (UV) and blue AlGaN/GaN/AlGaN double heterojunction structure light emitting diodes (LEDs) were electrically characterized using current-voltage (I-V) and capacitance-voltage (C-V) measurements as a function of frequency. An analysis of logarithmic plots of the forward I-V characteristics indicated that current in these diodes was proportional to V{sup}x, as opposed to e{sup}(qV/nkT), where x was observed to be either 1 or 2 at low biases increasing to as high as 40 at higher biases. The dependence of diode forward current on V{sup}x is likely to be due to space charge limited current in the presence of a high concentration of deep level states in the bandgap. The concentration of deep states and their position in the band gap were extracted from these logarithmic plots. For both the blue and the UV LEDs, several closely spaced levels were obtained, located most likely in the range between E{sub}v and E{sub}v+0.5eV with concentrations of the order of 10{sup}16/cm{sup}3 to 10{sup}17/cm{sup}3. Capacitance-voltage measurements as a function of frequency (200Hz-1MHz) at room temperature yielded a density of approximately 1×10{sup}15cm{sup}(-3) located at 0.46eV above the valence band-edge for both the UV and blue LED. Even though the location of these deep states from the I-V and C-V measurements are within the same range, the two orders magnitude difference in the concentration of deep states is not well understood at this point.