III-V semiconductor nanowires allow easy hetero-integration of optoelectronic components onto silicon due to efficient strain relaxation, well-understood design approaches and scalability. However continuous room temperature lasing has proven elusive. A key challenge is performing repeatable single-wire characterization { each wire can be different due to local growth conditions present during bottom-up growth. Here, we describe an approach using large-scale population studies which exploit inherent inhomogeneity to understand the complex interplay of geometric design, crystal structure, and material quality. By correlating nanowire length with threshold for hundreds of nanowire lasers, this technique reveals core-reabsorption as the critical limiting process in multiple-quantum-well nanowire lasers. By incorporating higher band-gap nanowire core, this effect is eliminated, providing reflectivity dominated behavior.
GaAsP nanowires (NWs) containing a range of different heterostructures are shown to be a highly promising system for the fabrication of efficient and novel ultra-small light emitters. NWs containing GaAs radial quantum wells (QWs) have emission with high thermal stability, due to both large electron and hole confinement potentials. A structure containing three QWs exhibits very low threshold lasing at low temperatures. Within the GaAsP central region of the same NW, the formation of quantum wires (QWRs) on three of the six vertices is observed, these QWRs are aligned parallel to the NW axis. The presence of twins causes a 180° rotation of the crystal about the growth axis, breaking the QWRs into short sections which may act as quantum dots (QDs). Optical studies of the NWs support the formation of optically active QWRs and QDs. In a second type of NW, during growth of the GaAsP NW core the introduction of a short GaAs section forms a QD. The inclusion of up to 50 QDs with high structural and optical quality is shown to be possible; indicating the potential for the fabrication of QD lasers. A structure with only one QD exhibits a single sharp emission line and behavior consistent with single exciton recombination. The addition of passivation layers, grown as a shell on the NW core, is shown to be essential in obtaining good optical properties. Our studies hence demonstrate that GaAsP-GaAs NWs containing heterostructures have significant potential for a range of novel light emitting applications.
Foreign-catalyzed assisted grown nanowires deteriorate the performance of optoelectronic devices because of incorporation of foreign impurities into the nanowires. We report on growth self-catalyzed p-type GaAs nanowires (NWs) with pure zinc blende (ZB) structure, and the fabrication of single-NW-based photodetector. The carrier mobility and concentration of GaAs field effect transistor are characterized both at room temperature and at low temperature respectively. Due to the absence of stacking faults and single crystal phase of the NWs, the photodetector exhibits room-temperature high photo-responsivity over than 105 A W-1 and great specific detectivity, which outperforms previously reported NW-based photodetectors. These results demonstrate that these self-catalyzed pure-ZB GaAs NWs to be promising candidates for optoelectronics applications. In addition, optoelectronic properties of single quantum dots embedded in single nanowires will be represented with an applied magnetic field.
Nanowires (NWs) have better functionality and superior performance as compared with the traditional thin film counterparts. However, NW growth is highly complicated and the growth mechanism is far from clear, especially when it is grown by vapor-liquid-solid mode. In this work, the influences of droplet size on the growth of self-catalyzed ternary NWs were studied using GaAsP NWs. The size-induced Gibbs−Thomson (GT) effect is observed for the first time in the self-catalyzed growth mode, which can make the smaller catalytic droplets have lower effective supersaturations. Thus, the droplet size can significantly influence the uniformity and composition of NWs. By carefully control the droplet size, the growth of highly uniform NW arrays are demonstrated. These results provide useful information for understanding the mechanisms of self-catalyzed III−V NW nucleation and growth with the important ternary III−V material systems.
Ternary GaAsP nanowires (NWs) have gained great attention due to their structure-induced novel properties and band gap that can cover the working wavelength from green to infrared. However, the growth and hence applications of selfcatalyzed GaAsP NWs are troubled by the difficulties in controlling P and the complexities in growing ternary NWs. In this work, self-catalyzed core-shell GaAsP NWs were successfully grown and demonstrated almost stacking-fault-free zinc blend crystal structure. By using these core-shell GaAsP NWs, single NW solar cells have been fabricated and a single NW world record efficiency of 10.2% has been achieved. Those NWs also demonstrated their potential application in water splitting. A wafer-scale solar-to-hydrogen conversion efficiency of 0.5% has been achieved despite the low surface coverage. These results open up new perspectives for integrating III−V nanowire photovoltaics on a silicon platform by using self-catalyzed GaAsP core−shell nanowires.
Self-catalyzed GaAsP nanowires (NWs) have a band gap that is capable of covering the working wavelengths from green to infrared. However, the difficulties in controlling P and the complexities of the growth of ternary NWs make it challenging to fabricate them. In this work, self-catalyzed GaAsP NWs were successfully grown on Si substrates by solid-source molecular beam epitaxy and demonstrated almost stacking fault free zinc blend crystal structure, Growth of high-quality shell has been realized on the core NWs. In the shell, a quasi-3-fold composition symmetry has been observed for the first time. Moreover, these growth techniques have been successfully applied for growth on patterned Si substrates after some creative modifications such as high-temperature substrate cleaning and Ga pre-deposition. These results open up new perspectives for integrating III−V nanowire photovoltaics and visible light emitters on the silicon platform using self-catalyzed GaAsP core−shell nanowires.
We realise growth of both GaAsP and GaAs core nanowires (NWs), as well as GaAsP core-shell NWs grown on (111) Si substrates using solid source molecular beam epitaxy (MBE). By modifying the growth conditions it is possible to change the dimensions of the GaAsP NWs and optimisation of these conditions yields high crystal quality structures. Scanning electron microscopy (SEM) as well as temperature, power and time resolved photoluminescence (PL) are used to study the optical and structural properties of the NWs. The incorporation of P into the NWs is used to shift the PL emission for ~ 810 nm to ~ 730 nm at 77 K, and also results in enhanced PL and an improved carrier lifetime. The addition of a p-doped GaAsP shell to a GaAsP core NW reduces the nonradiative recombination at surface states, as evidenced by x14 reduction of PL quenching with temperature, enhanced carrier lifetime, as well as a x3.5 increase in 77 K integrated PL intensity.
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