Effect of strain and barrier composition on the polarization of light emission from AlGaN/AlN quantum wells

Abstract

For AlGaN-based multi-quantum-well light emitters grown on c-plane substrates there is a tendency for the polarization of the emitted light to switch from transverse electric (TE) polarization to transverse magnetic (TM) polarization as the wavelength decreases. This transition depends on various factors that include the strain in the quantum well. Experimental results are presented that illustrate the phenomenon for nitride light emitting diodes (LEDs) grown on sapphire and on bulk AlN. Model calculations are presented which quantify the dependence of the TE/TM switch on the quantum well strain and the Al composition in the barriers surrounding the well.

Low-threshold stimulated emission at 249 nm and 256 nm from AlGaN-based multiple-quantum-well lasers grown on sapphire substrates

“…This result indicates the dominant band transition was between the conduction band and heavy hole band for the AlGaN MQW DUV lasers grown on the sapphire substrate emitting at 249 nm and 256 nm, thanks to the pseudomorphic growth and thus strong compressive strain in the MQWs. 24 The result is similar to the stimulated emission polarization measured from the AlGaN MQW DUV lasers grown on AlN substrates at similar emission wavelengths. 17 In summary, we have achieved room-temperature stimulated emission and laser operation from AlGaN-based MQW DUV heterostructures grown on (0001) sapphire substrates at 249 nm with a threshold of 61 kW/cm 2 and at 256 nm with a threshold of 95 kW/cm 2 .…”

Ultrawide‐Bandgap Semiconductors: Research Opportunities and Challenges

“…For ternary AlGaN materials as used in UV light emitters, a transition from TE to TM polarization occurs as the Al concentration increases. [266] Since TM-polarized light cannot be extracted parallel to the c-direction (the most commonly used growth direction for III-N materials), the performance of vertically-emitting UV LEDs degrades as Al content increases and wavelength decreases. Verticallyemitting lasers would be similarly affected.…”

Demonstration of transverse-magnetic deep-ultraviolet stimulated emission from AlGaN multiple-quantum-well lasers grown on a sapphire substrate

“…The small wavelength variation of $4 nm in the emission wavelengths of these lasers are due to lateral wafer inhomogeneities, which can include variation of strain state, composition, layer thickness, and carrier density. [15][16][17][18][19] As the excitation power density increased, the spectral linewidth narrowed significantly and reached FWHM values of 1.4-2.3 nm at respective maximum excitation power density, which indicated stimulated emission. 2,3 The laser thresholds were estimated to be 280, 250, and 290 kW/cm 2 for the 239-nm, 242-nm, and 243-nm lasers, respectively.…”