Midinfrared Photoluminescence up to 290 K Reveals Radiative Mechanisms and Substrate Doping-Type Effects of InAs Nanowires

Mid-infrared photoluminescence revealing internal quantum efficiency enhancement of type-I and type-II InAs core/shell nanowires

Internal quantum efficiency (IQE) is an important figure of merit for photoelectric applications. While the InAs core/shell (c/s) nanowire (NW) is a promising solution for efficient quantum emission, the relationship between the IQE and shell coating remains unclear. This Letter reports mid-infrared PL measurements on InAs/InGaAs, InAs/AlSb, and InAs/GaSb c/s NWs, together with bare InAs NWs as a reference. Analyses show that the IQE is depressed by a shell coating at 9 K but gets improved by up to approximately 50% for the InGaAs shell coating at 40 -140 K and up to approximately 20% beyond 110 K for the AlSb shell. The effect is ascribed not only to the crystal quality but more importantly to the radial band alignment. The result indicates the high-temperature IQE improvement of the type-I and type-II c/s NWs and the appropriateness of the mid-infrared PL analyses for narrow-gap NW evaluation.

Photoluminescence Characteristics of Zinc Blende InAs Nanowires

A detailed understanding of the optical properties of self-catalysed (SC), zinc blende (ZB) dominant, nanowires (NWs) is crucial for the development of functional and impurity-free nanodevices. Despite the fact that SC InAs NWs mostly crystallize in the WZ/ZB phase, there are very limited reports on the photoluminescence (PL) properties of ZB InAs NWs. Here, we report on the PL properties of Molecular Beam Epitaxy grown, SC InAs NWs. The as-grown NWs exhibit a dominant band to band (BtB) peak associated with ZB, InAs with an emission energy of ~0.41 eV in good agreement with the band gap energy of ZB InAs and significantly lower than that of the wurtzite phase (~0.48 eV). The strong BtB peak persists to near room temperature with a distinct temperature-dependent red-shift and very narrow spectral linewidth of ~20 meV (10 K) which is much smaller than previously reported values. A narrowing in PL linewidth with increasing NWs diameter is correlated with a decline in the influence of surface defects resulting from an enlargement in NWs diameter. This study demonstrates the high optical property of SC InAs NWs which is compatible with the Si-complementary metal-oxide-semiconductor technology and paves the way for the monolithic integration of InAs NWs with Si in novel nanodevices.

Enhanced luminescence properties of InAs nanowires via organic and inorganic sulfide passivation

InAs nanowires (NWs) have been considered to be highly suitable for future nanoscale photonic applications in mid-wave infrared region. However, progress in this area has been seriously hampered because of the poor radiative efficiency of InAs NWs attributed to their non-radiative (NR) surface. Herein, we demonstrated that a significant improvement of optical performances of InAs NWs grown by chemical vapor deposition could be achieved via sulfur passivation process. Luminescence properties of InAs NWs via organic sulfide (ODT) and inorganic sulfide ((NH₄)₂S) passivation were investigated by detailed photoluminescence (PL) measurement, which exhibited ∼17-fold enhancement in the intensity of optical emission compared to unpassivated InAs NWs. Moreover, the results of this investigation revealed that compared to ODT passivation, (NH₄)₂S passivation provided a more effective method to enhance the luminescence intensity even up to room temperature. This improvement of optical emission arises from the efficient passivation of surface defect states which act as competing NR centers. Furthermore, the stability of the passivated InAs NWs was investigated by PL measurement as a function of storage time in air. These findings are important for the successful implementation of optoelectronic devices based on InAs NWs.

Spatially resolved and two-dimensional mapping modulated infrared photoluminescence spectroscopy with functional wavelength up to 20 μm

The pixel-scale nonuniformity of the photoelectric response may be due either to the in-plane electronic inhomogeneity of the narrow-gap semiconductor or to the craft fluctuation during the fabrication process, which limits the imaging performance of the infrared focal plane array (FPA) photodetector. Accordingly, a nondestructive technique is most desirable for examining the spatial uniformity of the optoelectronic properties of the narrow-gap semiconductor to identify the origin of the FPA response nonuniformity. This article introduces a spatially resolved and two-dimensional mapping infrared photoluminescence (PL) technique, especially suitable for characterizing FPA narrow-gap semiconductors, based on the modulated PL method with a step-scan Fourier transform infrared spectrometer. The experimental configuration is described, and typical applications are presented as examples to a 960 × 640 μm² area of an InAsSbP-on-InAs layer in the medium-wave infrared range and a 960 × 960 μm² area of a HgTe/HgCdTe superlattice (SL) in the long-wave infrared range. The results indicate that, within a measurement duration of about 30 s/spectrum, a sufficiently high signal-to-noise ratio (SNR) of over 50 is achieved with a spectral resolution of 16 cm^-1 for the InAsSbP-on-InAs layer and a SNR over 30 is achieved with a spectral resolution of 12 cm^-1 for the HgTe/HgCdTe SL, which warrants reliable identification of the subtle differences among the spatially resolved and two-dimensional mapping PL spectra. The imaging of the in-plane distribution of PL energy, intensity, and linewidth is realized quantitatively. The results indicate the feasibility and functionality of the spatially resolved and two-dimensional mapping PL spectroscopy for the narrow-gap semiconductors in a wide infrared range.

Self-Seeded MOCVD Growth and Dramatically Enhanced Photoluminescence of InGaAs/InP Core-Shell Nanowires

We report on the growth and characterization of InGaAs/InP core-shell nanowires on Si-(111) substrates by metal-organic chemical vapor deposition (MOCVD). The strain at the core-shell interface induced by the large lattice mismatch between the InGaAs core and InP shell materials has strong influence on the growth behavior of the InP shell, leading to the asymmetric growth of InP shell around the InGaAs core and even to the bending of the nanowires. Transmission electron microscopy (TEM) measurements reveal that the InP shell is coherent with the InGaAs core without any misfit dislocations. Furthermore, photoluminescence (PL) measurements at 77 K show that the PL peak intensity from the InGaAs/InP core-shell nanowires displays a ∼ 100 times enhancement compared to the only InGaAs core sample without InP shell due to the passivation of surface states and effective carrier confinement resulting from InP shell layer. The results obtained here further our understanding of the growth behavior of strained core-shell heterostructure nanowires and may open new possibilities for applications in InGaAs/InP heterostructure nanowire-based optoelectronic devices on Si platform.