Polarization Matching in AlGaN-Based Multiple-Quantum-Well Deep Ultraviolet Laser Diodes on AlN Substrates Using Quaternary AlInGaN Barriers

Abstract

A prototypical design of AlGaN deep ultraviolet (DUV) laser diodes (LDs) on AlN substrates employing tapered electron blocking layer is presented. Two-dimensional optoelectronic simulation predicts lasing at a target wavelength of 250 nm. Degradation of optical gain associated with spatial separation of electron and hole wave functions inside the active region may be considerably reduced in designs featuring quaternary AlInGaN barriers, by virtue of polarization charge matching. A systematic method for selection of polarization-free quaternary barrier compositions is proposed for 250 nm DUV LD designs, accompanied by a sensitivity analysis. The selection procedure presented here is readily applied to LDs and light-emitting diodes operating at other wavelengths.Index Terms-AlN substrate, AlGaN active layer, deep ultraviolet (DUV) laser diodes (LDs), polarization charge, quantum-confined Stark effect (QCSE), quaternary barrier, tapered electron blocking layer (EBL).

AlGaN-Based Vertical Injection Laser Diodes Using Inverse Tapered p-Waveguide for Efficient Hole Transport

“…Previously, we have reported AlInN/AlInN [11] and AlGaN/AlInGaN [2] edge emitting LD designs operating at 250 nm wavelength. Our earlier investigations revealed that compositionally graded EBL [11] and polarization charge matched quantum well barriers (QWBs) [2] can significantly improve LD performance.…”

“…A detailed description of our simulation method can be found in previous publications [2], [11], and [20]. Simulation results presented in this article consider the compositiondependence of dopant activation energy [12]- [15], even in graded material, for accurate calculation of incomplete ionization of dopant species [21] throughout the epitaxial layer structure.…”

“…U LTRAVIOLET (UV) laser diodes (LDs) and light emitting diodes (LEDs) based on the wurtzite III-nitride material system fit the technological needs for a diverse list of present and future applications [1], [2]. Recently, they have been the focus of intense investigation by several photonic device research groups [3]- [10].…”

“…The design of vertical injection edge emitting LDs with stimulated emission in the UV-B (280-320 nm) and UV-C (< 280 nm) bands is fraught with numerous complications. A discussion of these issues may be found in the literature [2] and [11]. Among the most serious challenges is inefficient hole injection.…”

“…In order to reduce the problem of hole injection, several EBL designs are investigated and compared via numerical simulation. In this article, we suggest that superior hole injection can be achieved if a conventionally tapered EBL [2], [11], [16]- [19] is replaced by an inverse tapered p-waveguide layer whose bandgap decreases along the growth direction. This inverse tapering eliminates the aforementioned electrostatically induced artificial hole blocking layer, and leads to significantly lower threshold current.…”