Nonpolar light emitting diode with sharp near-ultraviolet emissions using hydrothermally grown ZnO on p-GaN

Abstract

Nonpolar n-ZnO/p-GaN heterojunction light emitting diode has been demonstrated with a-plane (112¯0) ZnO active layer grown by a facile low-cost solution growth method at low temperature of 90 °C. High quality nonpolar ZnO planar film without seed layer was directly formed on a-plane GaN template due to the anisotropic growth rates along the specific crystallographic directions. The turn on voltage of the device was as low as 3 V, and narrow stable UV-blue electroluminescence emissions with peak wavelength of 392 to 420 nm under various forward bias conditions at room temperature were observed.

Investigation on Hydrothermal Growth of a-Plane ZnO Using Epitaxial Lateral Overgrowth

“…As a result, nonpolar a-ZnO film lines are formed with remaining m-plane facets exposed on ELO window area. 2 As the growth process proceeds, a-ZnO grew over mask regions and spread to the c-axis direction for a-ZnO on the stripe patterns parallel to the m-axis, as shown in Fig. 2b, 2d, and 2f.…”

“…Recently, we have reported nonpolar a-plane ZnO (a-ZnO) film grown on a-plane GaN (a-GaN) template by hydrothermal method, which can act as a light-emitting active layer of nonpolar n-type ZnO/p-type GaN heterostructure LED. 2,15 However, the crystal quality of hydrothermally grown a-ZnO has much room for improvement compared with conventional GaN epitaxial layer. The growth mechanism also needs to be further understood.…”

“…Hydrothermal growth of a-ZnO on a-GaN template follows Volmer-Weber (VW) growth model which is also the growth mechanism of vapor phase epitaxy of GaN on sapphire substrate. 2,13 Three dimensional islands are formed at the initial growth stage since adatom-adatom interaction is stronger than that of the adatom with GaN surface. These islands continue to grow, and finally cause rough continuous films on the substrate.…”

“…In this crystal plane, there exist the spontaneous and piezoelectric polarizations inducing internal electric fields, which result in spatial separation of electron and hole wave functions. 1,2 This quantum confined stark effect causes the reduction in radiative recombination efficiency in quantum well structure. [3][4][5] As an alternative approach, extensive efforts have been exerted to eliminate the internal electric field using nonpolar or semipolar GaN crystals.…”

“…Nonpolar a-ZnO film was hydrothermally grown on ELO patterned a-GaN template by a simple aqueous solution method. 2 25 mM of zinc nitrate hexahydrate was dissolved in deionized water, and equimolar methenamine solution was mixed together in Teflon-lined autoclave. The substrate was placed in the growth solution at 90…”