Growth and characterization of Mg-doped AlGaN-AlN short-period superlattices for deep-UV optoelectronic devices

We report the growth and characterization of Mg-doped, short-period superlattices (Mg-SPSLs) consisting of AlN and Al(0.23)Ga(0.77)N epilayers grown by metal-organic vapor phase epitaxy. Superlattices with periods ranging from 10 to 25 angstrom and with an average Al composition of 0.42-0.74 were investigated. Optical transmission measurements showed that these structures have optical transparencies similar to random-alloy Al(x)Ga(1-x)N epilayers of the same average composition. X-ray diffraction (XRD) measurements confirmed that the period and average Al composition of the superlattices were in agreement with targeted values. Additionally. Mg doping of SPSL structures degraded or eliminated satellite peaks that were otherwise observed in the XRD scans of undoped or Si-doped SPSL structures, suggesting that the presence of Mg during growth alters the interfaces of the epilayers. P-type doping typically produced lateral resistivities of less than 10 ohm cm, and notably, a p-type resistivity of 6 ohm cm was measured in a Mg-SPSL structure with an average Al composition of 0.74. Analysis of temperature dependent resistivity showed an activation energy of 29 meV for a Mg-SPSL with an average composition of 0.62 and 18 meV for a Mg-SPSL with a composition of 0.49. The combined optical and electrical characteristics of these p-SPSLs suggest they could be potential candidates for wide bandgap p-type cladding layers in deep-UV laser diode structures. (C) 2010 Elsevier B.V. All rights reserved.