Tailoring the Lasing Modes in Semiconductor Nanowire Cavities Using Intrinsic Self-Absorption

Abstract

Understanding the optical gain and mode-selection mechanisms in semiconductor nanowire (NW) laser is key to the development of high-performance nanoscale oscillators, amplified semiconductor/plasmon lasers and single photon emitters, etc. Modification of semiconductor band structure/bandgap through electric field modulation, elemental doping or alloying semiconductors has so far gained limited success in achieving output mode tunability of the NW laser. One stifling issue is the considerable optical losses induced in the NW cavities by these extrinsic methods that limit their applicability. Herein we demonstrate a new optical self-feedback mechanism based on the intrinsic self-absorption of the gain media to achieve lowloss, room-temperature NW lasing with a high degree of mode selectivity (over 30 nm). The cadmium sulfide (CdS) NW lasing wavelength is continously tunable from 489 nm to 520 nm as the length of the NWs increases from 4 to 25 m. Our straightforward approach is widely applicable in most semiconductor or semiconductor/plasmonic NW cavities. Single crystalline semiconductor Fabry-Pé rot or whispering gallery nanowire (NW) cavity possessing naturally formed flat facets for good optical feedback is an ideal gain media for light amplification. [1][2][3][4][5][6][7][8][9][10] They are considered as one of the most important and promising routes to realizing miniaturized nanolasers and amplifiers. [11][12][13] Recent groundbreaking work on utilizing semiconductor NW cavities to compensate the damping loss and amplify the collective electron oscillations in plasmon nanocavities has kindled even greater interests in this field. 2,13,14 For practical applications, the ability to tailor the NW cavity mode is essential for developing multi-color miniaturized lasers, and critical for optimizing the resonant energy transfer between the cavity and the coupled system. 15 For a II-VI or III-V NW Fabry-Pé rot cavity, it is generally accepted that the output laser wavelength is determined by the bandgap of semiconductor NW. 11 To date, there is only limited success in tuning the optical cavity modes through (a) electric field modulation; and (b) elemental doping of the semiconductors. 6,9,16 In the former approach where the bandgap is modulated via the Franz-Keldysh or Stark effects, the NW cavities are highly susceptible to damage and only narrow tunability around 10 nm is demonstrated; 17 while in the later approach, the NW cavities are prone to structural defects induced by the dopants, thereby restricting the cavity gain. Keywords: Cadium sulfide, nanowire cavity, Urbach tail, Waveguide, lasingThough broadband tunable lasing wavelengths spanning 100 nm or more have been demonstrated in ternary semicondutor NW cavities, 18 cavity gain is however limited by the structural defects formed during the growth phase. 7,16 Use of extrinsic optical feedback such as photonic crystals to achieve better mode selectivity is another approach. However, the high-cost and complicated fabrication required, together with th...

Dual-color single-mode lasing in axially coupled organic nanowire resonators

“…Further investigation of the FSR in the PL spectra shows that the FSR is inversely proportional to the NW length ( L ), verifying the axially FP-type cavity resonances (fig. S8) ( 46 ). …”

Nanowire Lasers

“…This tuned the lasing wavelength from 706 to 746 nm upon selfabsorption of higher-energy photons by the nanowire and subsequent reemission of lower-energy photons, causing the emission wavelength to redshift. This method was also realized in CdS nanowires, where the lasing modes themselves could be similarly tailored [57]. An alternative method for wavelength tunability consists of making a heterostructure in the same way one achieves tunable sources with quantum wells [84] (see Section 4-b).…”

“…The Urbach tail is present when strong exciton-phonon interaction occurs, and thus "bends" the bandgap of the material, rendering it less sharp. The other reason is that these structures are good waveguides, con-fining the light in the structure longer, therefore increasing the probability of absorption [55,57]. Other parameters responsible for the broad Urbach tail, especially in 1D nanostructures, are crystallographic defects and surface states.…”

A room temperature low-threshold ultraviolet plasmonic nanolaser

“…The plasmonic cavities exhibit ultrasmall modal volume V m Bl 3 / 10-l 3 /1,000 (l is wavelength) enabling the tailoring of the strong light-matter interaction in a variety of linear (BQ/V m ) and nonlinear (BQ 2 /V m or Q/V m 1/2 ) optical process, where Q is the cavity quality factor. However, due to high intrinsic metal ohmic losses and radiation leakage, particularly in visible and ultraviolet regime, the Q ranges B10-100 which is still much smaller than their dielectric counterpart [20][21][22][23] . As a result, the threshold of optical-pumped visible plasmonic lasing (400-700 nm) is still nearly three orders higher than II-VI/III-VI semiconductor nanostructure photonic lasing.…”