1. Field of the Invention
This invention relates to semi-polar optoelectronic devices and methods of fabrication thereof, and in particular, semi-polar III-nitride optoelectronic devices on m-plane substrates with miscuts less than +/−15 degrees in the c-direction.
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by one or more reference numbers within brackets, e.g., [x]. A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
The anticipated high commercial demand for next-generation display technologies, such as miniature mobile projectors and high-definition fly-spot displays, has significantly accelerated the development of direct-emission green laser diodes (LDs). Technical criteria for such applications require LDs to have high efficiency, reliability, compactness, and modulation response capabilities [1]. While the wurtzite (Al,Ga,In)N-based material system is largely agreed upon as the leading candidate for green optoelectronic devices, a general consensus behind which crystal plane is optimal for epitaxial growth has yet to be reached.
Continuous-wave (CW) operation of LDs in the green spectral region has been demonstrated for devices grown on the conventional c-plane of GaN [2-4]. These devices, however, suffer from parasitic internal electric fields that give rise to the quantum-confined stark effect (QCSE) which decreases the quantum-well (QW) radiative recombination rate, and causes a blue-shift in emission wavelength with increasing carrier injection [5]. In addition, QCSE becomes more significant for long wavelength optoelectronic devices due to the increased lattice mismatch between the In-rich InGaN QWs and the barrier [2].
To circumvent polarization effects, researchers have demonstrated operation of LDs grown on the nonpolar m-plane orientation of the wurtzite crystal [6]. While a promising candidate for high power blue LDs, m-plane LDs has so far been limited to 500 nm lasing emission due to the formation of stacking faults in the active region [7-11].
Various semi-polar (or semipolar) planes, such as (10-11) and (11-22), have been also investigated as alternative growth planes [12-13]. Recently, researchers have reported lasing in the green spectral region from high quality InGaN QWs grown on the semi-polar (20-21) plane [14-15]. Further studies have shown that green emitting QWs grown on (20-21) exhibit high compositional homogeneity with localization energy values lower than that reported for c-plane [16]. However, quaternary AlInGaN cladding layers were needed in (20-21) LDs to achieve sufficient modal confinement without generating strain-induced misfit dislocations (MDs) [17]. While the use of quaternary AlInGaN cladding layers presents a solution for semi-polar planes with low critical thickness, a simple AlGaN cladding-free structure with high composition InGaN waveguides would be much more attractive from a mass-production point of view [7, 15, 18].
What is needed are improved methods for optoelectronic device growth. The present invention satisfies this need.