Effects of modulation doped n-AlGaN epilayers on the optoelectronic properties of 278-nm AlGaN-based flip-chip light-emitting devices

AlGaN-based deep ultraviolet flip-chip light-emitting diodes (DUV-FCLEDs), have been fabricated by different doping processes in n-AlGaN epilayers, respectively. That is, the silicon uniformly doped (Si-UD) processes and the modulation doped (MD) growth methods. Compared with the UD sample of about 278-nm emission wavelength, the electrical structures, optical properties and output performance of the MD sample, have been effectively enhanced. The MD sample is a more intense UV emitter than the UD sample by a factor of about 30% in the electroluminescence intensities, the photoluminescence spectra also demonstrate that the MD methods can effectively enhance the light emissions. The measured peak capacitance of internal capacitance–voltage characteristics in the UD sample is only 175 pF at room temperature, while the MD sample is about 390 pF, which is mostly attributed to the series capacitors effects within the periodic n-AlGaN super-lattices structures. Both the forward bias voltage and reverse leakage current of the MD sample are directly reduced than those of the UD sample, and the calculated conductance is significantly increased. We demonstrate that there are higher current spreading efficiency and better devices’ reliability in the MD sample with the Si-MD processes. Our investigations may be useful for the enhancements of structure and optoelectronic performance in DUV-FCLEDs succeeding the MD methods in n-AlGaN epi-layers.