Novel Ohmic Contact Technology to P-type and N-type GaN

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The specific resistance of ohmic contacts to n- and p-type GaN, AlGaN, and GaInN are very important for many device properties such as power efficiency, amplification, noise, device heating, and reliability. In this work, a fundamentally novel approach to low-resistance ohmic contacts to AlGaN, GaInN, and GaN will be developed and investigated. The contacts are based on the employment of the strong spontaneous and piezoelectric polarization fields occurring in GaN and related compounds. The polarization fields in the near-surface layers of metal-semiconductor contacts will enhance the tunneling probability of carriers thereby reducing the ohmic contact specific resistance. The theory and modeling pertaining to tunneling probability, contact formation, and specific contact resistance will be developed. Polarization-enhanced contacts will be demonstrated and reduced contact resistances will be verified. In addition, the role of polarization fields in AlGaN-GaN superlattices will be investigated and the superlattices will be optimized for ohmic contact applications. An integral part of the work will be the incorporation of the polarization-enhanced ohmic contacts in optoelectronic and electronic devices. Light-emitting diodes (LEDs), in particular LEDs used for high-power illumination applications, are in need of low resistance ohmic contacts in order to reduce device heating and improve device efficiency and reliability. GaN/GaInN LEDs with polarization-enhanced ohmic contacts will be demonstrated. Polarization-enhanced ohmic contacts will also be realized in lasers and transistors and improved properties of these devices will be demonstrated.******************************************************************