Growth and characterization of wurtzite InP/AlGaP core–multishell nanowires with AlGaP quantum well structures

Abstract

We report on selective-area growth and characterization of wurtzite (WZ) InP/AlGaP core-multishell nanowires. Quantum well (QW) structures were fabricated in the AlGaP multishells by changing alloy compositions. Transmission electron microscopy revealed that the AlGaP multishell was grown with a WZ structure on side of the WZ InP core. The lattice constants of the WZ InP core and WZ AlGaP shell were determined by X-ray diffraction. Cathodoluminescence studies showed that the WZ AlGaP QW with an Al composition of 20% had green emissions at 2.37 eV. These results open the possibility for green light-emitting diodes using WZ AlGaP based materials. 2Color mixed RGB light-emitting diodes (LEDs) are promising candidates for future solidstate lightning and display technology due to their potential advantages in energy conversion efficiency and color rendering index (CRI). 1,2) However, achieving high efficient LEDs in the green region is challenging due to a lack of suitable semiconductor materials, which is known as the "green gap". 3,4) Non-nitride III-V materials having wurtzite (WZ) structures have recently offered a new approach to overcome this issue. Some theories predict that GaP and AlP in the WZ structures have direct band gaps in contrast to the conventional zinc blende (ZB) structures with indirect band gaps. [5][6][7] Although this approach has been experimentally demonstrated in WZ GaP 8,9) and WZ AlInP, 10) these WZ materials with quantum well (QW) structures required for LED applications have not been reported so far.In nanowire (NW) structures, radial core-multishell (CMS) NWs with QW structures are suitable structures for LED applications. 11,12) In this study, we report the growth and characterization of WZ InP/AlGaP CMS NWs with QW structures for the green color spectrum. The WZ AlGaP at an Al composition of around 20% is expected to have the band gap energy in the green spectral region according to calculations of their band structures. 6,7) The CMS NWs were synthesized by selective-area metal organic vapor phase epitaxy (SA-MOVPE). In SA-MOVPE, InP NWs can be grown with a pure WZ structure by properly adjusting the growth conditions. 13-15) Based on these WZ InP NWs, the crystal structure transfer method [16][17][18] was applied for the radial multishell growth. At first, a 20-nm-thick SiO 2 layer was deposited on an InP (111)A substrate using plasma sputtering, and the SiO 2 layer was partially removed using electron-beam (EB) lithography and wet chemical etching. The SiO 2 patterns were designed to be a periodic array of openings with a diameter of 130 nm.The SA-MOVPE was performed in a low-pressure MOVPE reactor using trimethylaluminum (TMAl), trimethylgallium (TMGa), trimethylindium (TMIn), and tertiarybutylphosphine 3 (TBP) as source materials. Prior to the growth, the native oxide on the openings was removed using thermal cleaning for 5 min at 600°C under a hydrogen and TBP ambient. After thermal cleaning, WZ InP NWs were grown for 15 min at 660°C with a V/III ratio of 18, which is t...

Radial Growth Evolution of InGaAs/InP Multi-Quantum-Well Nanowires Grown by Selective-Area Metal Organic Vapor-Phase Epitaxy

“…25 This is consistent with the SAE growth of InP/ AlInP core−shell and GaP/AlGaP core−shell NWs, where top segments had a ZB structure, while the shells had a WZ structure consistent with the core. 12,13 Similarly, the axial InP barriers adopted the WZ phase, in agreement with the base InP grown in identical conditions.…”

“…Basically the (0001) plane of WZ InP used as a growth template for axial QWs is nearly identical to the ZB (111) plane, and each InGaAs QW growth initiates the ZB phase . This is consistent with the SAE growth of InP/AlInP core–shell and GaP/AlGaP core–shell NWs, where top segments had a ZB structure, while the shells had a WZ structure consistent with the core. , Similarly, the axial InP barriers adopted the WZ phase, in agreement with the base InP grown in identical conditions.…”

“…Heurlin et al reported WZ InP/InGaAs NW core–shell heterostructures with light emission at ∼1.4 μm . Ishizaka et al have successfully grown WZ InP/GaP core–shell NWs, InP/AlGaP core–shell NWs, and InP/AlInP core–shell NWs for green light emission by employing the core WZ InP NW as a template to transfer the crystal structure to radially grown heterostructures. Recently Chang-Hasnain’s group reported optically pumped lasing at ∼1.3 μm and array LEDs with ∼1.5 μm from core–shell InGaAs/InP MQW nanopillars grown on Si by the SAE technique, demonstrating a great potential for achieving InGaAs QW-NW devices for optical communications.…”

Realization of Wurtzite GaSb Using InAs Nanowire Templates

“…We here report on successful growth of wurtzite GaSb using wurtzite InAs nanowires as templates for radial (shell) growth, the so‐called crystal structure transfer method . GaSb shell thickness up to 30–40 nm is demonstrated, which is controllable with growth time.…”

“…One method is to use a high V/III ratio of the precursors for growth of zinc blende, while using a much lower value for the wurtzite structure . Alternative approaches such as control of nanowire diameter, content of a specific material such as Sb during growth, and crystal structure transfer method, are reported for other materials. Having control over the crystal structure is important since it strongly affects the physical properties of the material .…”