Effect of indium in Al_0.65Ga_0.35N/Al_0.8Ga_0.2N MQWs for the development of deep‐UV laser structures in the form of graded‐index separate confinement heterostructure (GRINSCH)

Abstract

AlGaN‐based graded‐index‐separate‐confinement‐heterostructures (GRINSCHs) with Al0.65Ga0.35N/Al0.8Ga0.2N MQWs in their active region were grown by plasma‐assisted MBE on (0001) 6H‐SiC substrates. The MQWs were grown under excess Ga. Indium flux was used in addition in some of the samples in order to study the role of indium on the growth mode of such MQWs. Transmission electron microscopy (TEM) provides evidence that the bottom compositionally graded AlGaN layer in the GRINSCH structure may also be serving as a strain transition buffer layer, by blocking threading defects in the vicinity of the AlN/AlGaN heterointerface. X‐ray diffraction (XRD) indicates that the interfaces in the MQWs grown in the presence of indium are sharper. However, photoluminescence (PL) studies indicate evidence of stimulated emission at relatively low threshold only in the sample grown without indium, which is attributed to deep band structure potential fluctuations in this sample. The presence of indium during growth led to more homogeneous AlGaN MQWs, which require higher excitation flux to produce population inversion.

Ultraviolet optoelectronic devices based on AIGaN alloys grown by molecular beam epitaxy

“…[54] On the other hand, this sample was grown under Ga-rich conditions. One possibility is that the Indium dissolves in the liquid Ga in the surface of the growing AlGaN film and forms Ga-In liquid solution, [129] which wets better the AlGaN seed than pure liquid Ga and forms a uniform in thickness Ga-In liquid film covering the AlGaN seed. Thus, Al and active nitrogen dissolving into the liquid Ga-In film lead to laterally homogeneous AlGaN film.…”

“…[129,[134][135][136] Such laser device structures were successfully used in traditional III-V compounds and were found to have the lowest threshold current. Besides the efficient carrier and optical field confinement in lasers based on the GRINSCH configuration, such laser designs based on AlGaN alloys have the additional advantage of automatically leading to a p-n junction formation, [134] owing to opposite compositional grading of the AlGaN alloys in either side of the active region of the device.…”

“…[136] The crystal microstructure and optical properties of such GRINSCH devices can be found in the original papers. [129,[134][135][136] …”

Growth mode of nitride semiconductors on nano‐patterned sapphire substrates by molecular beam epitaxy

“…The exact origin of the stronger peak at 350 nm is not clear. It could be due to band structure potential fluctuations in the AlGaN alloy [11][12][13][14][15][16], emission from the inclined facets under the surface of the film, or recombination through point defect such as oxygen impurity. The integrated CL intensity in the patterned region is 16 times higher than that in the un-patterned region of the substrate.…”

Graded-Index Separate Confinement Heterostructure AlGaN Nanowires: Toward Ultraviolet Laser Diodes Implementation

“…19, 20 , 21 Most importantly, polarization-induced three-dimensional (3D) electron and hole gases can be created by introducing a compositional AlGaN grading profile, instead of an abrupt AlGaN heterojunction. 22,23,24,25 Such 3D free electrons and holes usually originate from donor-and acceptor-like impurities or defects via polarization-induced ionization process, and have been implemented in AlGaN-based planar UV emitters 26,27,28 without any intentional doping. 23 Compared to the AlGaN epitaxial thin-film layers, p-type AlGaN nanowires were recently found to have lower resistivity owing to more efficient Mg incorporation and lower activation energy which are caused by the reduced lattice strain imposed by surface dopants, compared to bulk dopants.…”