We demonstrate room temperature continuous wave lasing in bottom-up photonic crystal cavities formed by patterned III-V nanopillars. Single-cell high-Q photonic crystal cavities are formed with nanopillars by selective-area epitaxy. Control of the nanopillar geometry and heterostructures allows for high-Q and large confinement factor, resulting in a low threshold power density of 75 W/cm^2 at 1040 nm emission wavelength

Huffaker, D. L.

Kim, S.-H.

Liang, B. L.

Lin, A.

Scherer, A.

Scofield, A. C.

Shapiro, J. N.

A.C. Scofield

S-H Kim

J.N. Shapiro

A. Lin

B.L. Liang

A. Scherer

D.L. Huffaker

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Room Temperature Continuous Wave Lasing in Nanopillar Photonic Crystal Cavities

Caltech Authors - Main

CTh4M.2.pdf CLEO Technical Digest © OSA 2012
Room Temperature Continuous Wave Lasing in Nanopillar 
Photonic Crystal Cavities 
A.C. Scofield1,a, S-H Kim2, J.N. Shapiro1, A. Lin1, B.L. Liang1, A. Scherer2, and D.L. Huffaker1,b 
1Department of Electrical Engineering and California NanoSystems Insitute, University of California Los Angeles, Los Angeles, CA, 90095, USA 
2Department of Electrical Engineering and Kavli Nanoscience Institute, California Institute of Technology, Pasadena, CA, 91125, USA 
aE-mail address: ascofield@ucla.edu, bE-mail address: huffaker@ee.ucla.edu 
Abstract: We demonstrate room temperature continuous wave lasing in bottom-up photonic 
crystal cavities formed by patterned III-V nanopillars. Single-cell high-Q photonic crystal cavities 
are formed with nanopillars by selective-area epitaxy. Control of the nanopillar geometry and 
heterostructures allows for high-Q and large confinement factor, resulting in a low threshold 
power density of 75 W/cm2 at 1040 nm emission wavelength. 
OCIS codes: (230.5298) Photonic crystals; (140.3945) Microcavities 
1. Introduction 
Continuing development in the area of nanowire (NW) and nanopillar (NP) based optoelectronic devices has grown 
dramatically in recent years. The ability to control the formation of axial and radial heterostructures during growth, 
as well as the ability to grow on large lattice mismatched substrates such as Silicon has been a large motivating 
factor1. However, the demonstration of low threshold lasers with NWs or NPs as the active gain medium has been 
limited due to difficulty in design and fabrication of high quality optical cavities. Furthermore, the small diameters 
of these semiconductor nanostructures results in high surface recombination rates. Here, we present a method of 
fabricating photonic crystal (PhC) cavities with selective-area epitaxy of III-V NPs. The ability to control position, 
diameter, axial and radial heterostructures allows for the formation of high-Q cavities with low-threshold capable of 
continuous wave lasing at room temperature. 
2. Design and fabrication 
The design of the NP-PhC cavities is shown in Fig 1. The NPs are embedded in low index polydimethylsiloxane 
(PDMS) with one side of the cavity exposed to air. The NPs are arranged in a triangular lattice with a radius to pitch 
ratio (r/a) of 0.2 to ensure a wide photonic band gap. Five rows of NPs are shifted towards the center of the cavity as 
shown in Fig 1a. The shift factors resulting in the optimum cavity Q of 10,700 is shown in Fig 1b. The E-field 
intensity of the resulting mode is shown in Fig 1c. 
 
Figure 1. Design of high-Q PhC cavities composed of NPs. (a) Rows of NPs surrounding the center of the cavity are shifted towards the 
center to form a single resonant mode. (b) The lattice shift in units of lattice constant a for each row of the cavity for maximum Q. (c) E-field 
intensity of the cavity mode. 
 The NPs forming the PhC lasers are grown by selective-area metal-organic chemical vapor deposition on 
masked GaAs substrates2. The NPs implement a GaAs/InGaAs/GaAs axial double heterostructure for accurate 
placement of gain with the the cavity3 and InGaP shells to reduce surface recombination4. Fig 2a shows the NP-PhC 
CTh4M.2.pdf CLEO Technical Digest © OSA 2012
cavities embedded in PDMS with a close-up view showing the axial and radial heterostructures. This design allows 
for excellent overlap between the InGaAs gain region and the peak E-field intensity of the cavity mode. 
 
Figure 2. (a) Schematic of the NP-PhC in PDMS with close-up showing the GaAs/InGaAs/GaAs axial heterostructure with InGaP shells. (b) 
45° tilted SEM of a NP-PhC cavity as grown on the GaAs substrate with a magnified top-down view of the cavity region. (c) L-L curve of a NP-
PhC laser under continuous excitation at room temperature with inset showing the output spectrum at 5×Lth. 
3. Results 
A NP-PhC cavity as grown on the GaAs substrate is shown in Fig 2b. The inset shows a top-down view of the cavity 
matching the high-Q design shown in Fig 1. Based on growth rate calibrations, the GaAs segments are estimated to 
be 200 nm in height, with the center InGaAs segment ~130 nm in height. With an experimental cavity Q of ~8000 
and a simulated confinement factor of Γ = 0.328, the required threshold gain for lasing is calculated to be gth = 76 
cm-1.  
The experimental demonstration of continuous wave lasing at room temperature is shown in Fig 2c. The L-L 
curve spans from 0.2×Lth to 5×Lth where Lth = 60 µW. With a 10 µm diameter spot size of the excitation laser, the 
resulting threshold power density is 75 W/cm2. Above a maximum input power of 300 µW the NPs quickly degrade 
due to heating as a result of the relatively low thermal conductivity of PDMS. The inset of Fig 2c shows the output 
spectrum above threshold with the peak emission wavelength at 1040 nm.  
In conclusion, we have demonstrated room temperature continuous wave lasing in NP-PhC cavities. The low 
threshold power achieved is a result of accurate control of the NP heterostructures and geometry. These lasers 
embedded in PDMS can be useful as internal light sources in for spectroscopy in microfluidic and biosensing 
systems. Future work will explore use of transparent conducting oxides (TCOs) as contacts for electrically injected 
lasers.   
4. References 
[1] K. Tomioka, Y. Kobayashi, J. Motohisa, S. Hara, T. Fukui. Nanotechnology 20 (2009) 145302 
[2] P.N. Senanayake, A. Lin, G. Mariani, J.N. Shapiro, C. Tu, A.C. Scofield, P.S. Wong, B.L. Liang, D.L. Huffaker. Appl. Phys. Lett. 2010, 97, 
203108 
[3] J.N. Shapiro, A. Lin, P.S. Wong, A.C. Scofield, C. Tu, P.N. Senanayake, G. Mariani, B.L. Liang, D.L. Huffaker. Appl. Phys. Lett. 2010, 97, 
243102 
[4] A.C. Scofield, J.N. Shapiro, A. Lin, A.D. Williams, P.S. Wong, B.L. Liang, D.L. Huffaker. Nano Lett. 2011, 11, 2242 


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Room Temperature Continuous Wave Lasing in Nanopillar Photonic Crystal Cavities

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