Valence band engineering for remarkable enhancement of surface emission in AlGaN deep‐ultraviolet light emitting diodes

Valence band engineering for remarkable enhancement of surface emission in AlGaN deep‐ultraviolet (UV) light emitting diodes (LEDs) has been theoretically investigated by the calculation using the 6×6 k·p Hamiltonian. It has already been pointed out that the topmost valence band in deep‐UV AlGaN material has a Z‐like character and this causes the c‐axis polarized emission unfavourable for light extraction from c‐plane based LEDs. We have found, in this study, that this unfavourable polarization can be switched into favourable in‐plane polarization by decreasing quantum well (QW) width and/or introducing in‐plane compressive strain, which cause band‐crossing and change the character of the topmost band. It is also shown that such polarization changes occur in the QWs on semipolar substrates although that does not take place in those on nonpolar substrates. Furthermore, we have derived the condition of the polarization switch as an approximate analytical expression which could be useful for device structural design. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)