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ring device
Microelectronics Journal 36 (2005) 298–300 www.elsevier.com/locate/mejo
Photonic quantum corral, carrier ordering, and photonic quantum dot/ring device O’Dae Kwon, M.J. Kim, S.-J. An, D.K. Kim, S.E. Lee* Department of Electronic and Electrical Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, South Korea Available online 18 April 2005
Abstract This study aims at firstly introducing a theoretical background of photonic quantum ring naturally formed by photonic quantum corral effect in the 3D Rayleigh–Fabry–Perot micro-cavity. This unique phenomenon is visualized as polar angle-dependent multi-chromatic emission spectra corresponding to an each lightwave with different optical paths. Also, we fabricated an H-D structure for a single PQR, i.e. single mode within a luminescent wavelength region and ultra-low threshold 16-K PQR laser array for such as free space optical interconnections. q 2005 Elsevier Ltd. All rights reserved. Keywords: Photonic quantum ring; Photonic quantum corral effect; H-D structure
1. Introduction The quantum well (QW) or wire (QWR) confinement gives rise to discrete energy states and a step- or spike-like density-of-state profile in the active region, whose technical advantages may be applied for high density chip fabrications, lower threshold current and power consumption [1–3]. However, the formation technology of nano-scale patterning and the growth technology of controllable quantum structures still remain troublesome in the uniformity of shape, size, density, and compositions. In this paper we report a naturally produced photonic quantum ring (PQR) devices, which exhibit ideal quantum wire properties, in termpof ffiffiffiffi ultra-low threshold currents and QWR properties of T -dependent spectral shifts. We also report a hyperboloid-drum (H-D) structure for electrically pumped nano-scale PQR laser.
2. Photonic quantum ring We demonstrate that an ideal QWR nature can be achieved from a toroidal micro-cavity of new 3D * Corresponding author. Tel.: C82 54 279 2212; fax: C82 54 279 8119. E-mail address: [email protected] (O’Dae Kwon).
0026-2692/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.mejo.2005.02.083
Rayleigh–Fabry–Perot (RFP) whispering gallery (WG) modes in the peripheral region (Fig. 1(a)) of a pillar-shaped micro-cavity laser containing the active MQW planes between the top (p-type) and bottom (n-type) distributed Bragg reflector (DBR) layers (Fig. 1(b)). The PQR laser forms a toroidal cavity type WG mode under a 3D RFP condition composed of a vertical confinement of photons by the DBR layers and an annular confinement of photons by total internal reflection occurring along the lateral boundaries of a PQR laser disk, as in a microdisk laser [4–6]. Dynamic steady state carriers on the MQW active planes within the toroidal cavity are re-distributed in the form of concentric circles of quantum wires (QWRs), which result in the photonic quantum rings before the imminent recombination, in accordance to a photonic quantum corral effect (PQCE) [7]. The dimensional reduction from QW planes to the PQR manifold within the toroid, via lightwave-trapped formations of l/2 spaced photonic quantum-corral manifold, takes place due to the standing mode influences of helical intracavity lightwave [8,9]. The PQR’s helical manifold lightwaves of multi-angle resonant paths in the toroidal cavity can be visualized as a function of view angle (qv), defined by the polar orientation from the surface normal of the device, in terms of spectral characteristics and non-equal intermode spacing [10]. The emission spectra for a PQR laser of diameter fZ15 mm, collected at view angles of qvZ10 and 208, are shown in Fig. 2. Each spectrum has an envelope of w6 nm span containing several discrete modes
O.D. Kwon et al. / Microelectronics Journal 36 (2005) 298–300
Fig. 1. (a) CCD image of the PQR laser (diameter fZ15 mm, IZ10 mm) showing the light emission from the peripheral ring and (b) the SEM photographs of the PQR laser diode structure.
corresponding to each PQR manifold with different reflection angles in the toroidal cavity. The envelope of the spectrum is blueshifted as the qv increases, but the individual modes in the overlapped enveloped range match each other well. With these properties described above,pffiffiffiultra-low threshold ffi currents and QWR properties of T -dependent spectral shifts, which are critical factors for high-density chip applications like optical interconnects [4].
3. H-D structure and PQR lasers array The number (c) of concentric PQR manifolds in the Rayleigh’s WG band is simply given by [4,5] 2n f n cZ ! 1 K eff l 2 n where n is the refractive index of the active medium, neff is the effective refractive index in the f direction [11] of a conformal transform to rectangular coordinate and f is the diameter of PQR laser. For the PQR laser of about 6 mm or smaller diameter we can obtain a single quantum ring, i.e. cZ1, possibly leading to a single mode lasing. Additionally, for the purpose of lower threshold PQR lasing we fabricated a hyperboloid-drum (H-D) structure (Fig. 3) with 3.0x10-9
Fig. 3. The SEM photographs of the H-D structure PQR laser diode with an active diameter fZ95 nm.
a 95 nm diameter. This structure can be applied to develop an electrically pumped laser with very small active-layer diameter, while maintaining a wide contact area for easy electrical connection. Details of the fabrication and structurepffiffiffiare ffi described elsewhere [12]. Also, the PQR laser’s T -dependent spectral shifts lend itself easily to large-scale integrations, and the ultra-low threshold currents permit room-temperature CW operation of high density arrays. A microscopic picture of the 16-K PQR array showing 98% yield is given in Fig. 4, corresponding to a driving current of 16 mA, or 1 mm per each PQR laser cell with fZ3 mm.
4. Conclusion We have shown that an ideal QWR nature can be realized from a toroidal micro-cavity of 3D Rayleigh–Fabry–Perot PQR modes in the peripheral region of the active MQW
λ0
Intensity (a. u.)
θv = 10°
2.0x10-9 θv = 20°
1.0x10-9
0.0 838
840
842
844
846
Wavelength (nm) Fig. 2. Multi-chromatic spectra collected at view angles qvZ10 and 208. l0 is a surface normal direction resonant mode of device.
299
Fig. 4. 16-K (128!128) PQR laser diode array.
300
O.D. Kwon et al. / Microelectronics Journal 36 (2005) 298–300
planes due to the PQCE. pffiffiffiffi Ultra-low threshold currents and QWR properties of a T -dependent spectral shifts allow us to make an H-D structure for the single PQR mode and high density PQR laser array chips.
Acknowledgements This research is supported by Samsung Co., National Research Laboratory, the BK21, and KOSEF projects of the Korean government.
References [1] E. Kapon, Quantum Well Lasers, in: P.S. Zory (Ed.), Academic, London, 1993.
[2] C. Wilmsen, H. Temkin, L.A. Coldren, Vertical-Cavity Surface Emitting Lasers, Cambridge University Press, New York, 1999. [3] A. Yariv, Appl. Phys. Lett. 53 (1988) 1033. [4] J.C. Ahn, K.S. Kwak, B.H. Park, H.Y. Kang, J.Y. Kim, O.D. Kwon, Phys. Rev. Lett. 82 (1999) 536. [5] B.H. Park, J.C. Ahn, J. Bae, J.Y. Kim, M.S. Kim, S.D. Baek, O.D. Kwon, Appl. Phys. Lett. 79 (2001) 1593. [6] S.L. McCall, A.F.J. Levi, R.E. Slusher, S.J. Pearton, A. Logan, Appl. Phys. Lett. 60 (1992) 289. [7] G. Francs, C. Girard, J. Marvig, J.C. Weeber, C. Chicane, T. David, T. Dereux, D. Peyrade, Phys. Rev. Lett. 86 (2001) 4950. [8] O.D. Kwon, M.S. Kim, B.H. Park, D.H. Park, Tech. Dig. QELS (2000); 133. [9] B.H. Park, J. Bae, M.J. Kim, O.D. Kwon, Appl. Phys. Lett. 81 (2002) 580. [10] J.W. Bae, J.W. Lee, O.D. Kwon, V.G. Minogin, Opt. Lett. 28 (2003) 1861. [11] M.K. Chin, D.Y. Chu, T. Ho, J. Appl. Phys. 75 (1994) 3302. [12] J.Y. Kim, S.J. An, J.Y. Kim, J.W. Lee, B.K. Kang, O.D. Kwon, J. Vac. Sci. Technol. B 22 (2004) 673.
Photonic quantum corral, carrier ordering, and photonic quantum dot/ring device O’Dae Kwon, M.J. Kim, S.-J. An, D.K. Kim, S.E. Lee* Department of Electronic and Electrical Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, South Korea Available online 18 April 2005
Abstract This study aims at firstly introducing a theoretical background of photonic quantum ring naturally formed by photonic quantum corral effect in the 3D Rayleigh–Fabry–Perot micro-cavity. This unique phenomenon is visualized as polar angle-dependent multi-chromatic emission spectra corresponding to an each lightwave with different optical paths. Also, we fabricated an H-D structure for a single PQR, i.e. single mode within a luminescent wavelength region and ultra-low threshold 16-K PQR laser array for such as free space optical interconnections. q 2005 Elsevier Ltd. All rights reserved. Keywords: Photonic quantum ring; Photonic quantum corral effect; H-D structure
1. Introduction The quantum well (QW) or wire (QWR) confinement gives rise to discrete energy states and a step- or spike-like density-of-state profile in the active region, whose technical advantages may be applied for high density chip fabrications, lower threshold current and power consumption [1–3]. However, the formation technology of nano-scale patterning and the growth technology of controllable quantum structures still remain troublesome in the uniformity of shape, size, density, and compositions. In this paper we report a naturally produced photonic quantum ring (PQR) devices, which exhibit ideal quantum wire properties, in termpof ffiffiffiffi ultra-low threshold currents and QWR properties of T -dependent spectral shifts. We also report a hyperboloid-drum (H-D) structure for electrically pumped nano-scale PQR laser.
2. Photonic quantum ring We demonstrate that an ideal QWR nature can be achieved from a toroidal micro-cavity of new 3D * Corresponding author. Tel.: C82 54 279 2212; fax: C82 54 279 8119. E-mail address: [email protected] (O’Dae Kwon).
0026-2692/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.mejo.2005.02.083
Rayleigh–Fabry–Perot (RFP) whispering gallery (WG) modes in the peripheral region (Fig. 1(a)) of a pillar-shaped micro-cavity laser containing the active MQW planes between the top (p-type) and bottom (n-type) distributed Bragg reflector (DBR) layers (Fig. 1(b)). The PQR laser forms a toroidal cavity type WG mode under a 3D RFP condition composed of a vertical confinement of photons by the DBR layers and an annular confinement of photons by total internal reflection occurring along the lateral boundaries of a PQR laser disk, as in a microdisk laser [4–6]. Dynamic steady state carriers on the MQW active planes within the toroidal cavity are re-distributed in the form of concentric circles of quantum wires (QWRs), which result in the photonic quantum rings before the imminent recombination, in accordance to a photonic quantum corral effect (PQCE) [7]. The dimensional reduction from QW planes to the PQR manifold within the toroid, via lightwave-trapped formations of l/2 spaced photonic quantum-corral manifold, takes place due to the standing mode influences of helical intracavity lightwave [8,9]. The PQR’s helical manifold lightwaves of multi-angle resonant paths in the toroidal cavity can be visualized as a function of view angle (qv), defined by the polar orientation from the surface normal of the device, in terms of spectral characteristics and non-equal intermode spacing [10]. The emission spectra for a PQR laser of diameter fZ15 mm, collected at view angles of qvZ10 and 208, are shown in Fig. 2. Each spectrum has an envelope of w6 nm span containing several discrete modes
O.D. Kwon et al. / Microelectronics Journal 36 (2005) 298–300
Fig. 1. (a) CCD image of the PQR laser (diameter fZ15 mm, IZ10 mm) showing the light emission from the peripheral ring and (b) the SEM photographs of the PQR laser diode structure.
corresponding to each PQR manifold with different reflection angles in the toroidal cavity. The envelope of the spectrum is blueshifted as the qv increases, but the individual modes in the overlapped enveloped range match each other well. With these properties described above,pffiffiffiultra-low threshold ffi currents and QWR properties of T -dependent spectral shifts, which are critical factors for high-density chip applications like optical interconnects [4].
3. H-D structure and PQR lasers array The number (c) of concentric PQR manifolds in the Rayleigh’s WG band is simply given by [4,5] 2n f n cZ ! 1 K eff l 2 n where n is the refractive index of the active medium, neff is the effective refractive index in the f direction [11] of a conformal transform to rectangular coordinate and f is the diameter of PQR laser. For the PQR laser of about 6 mm or smaller diameter we can obtain a single quantum ring, i.e. cZ1, possibly leading to a single mode lasing. Additionally, for the purpose of lower threshold PQR lasing we fabricated a hyperboloid-drum (H-D) structure (Fig. 3) with 3.0x10-9
Fig. 3. The SEM photographs of the H-D structure PQR laser diode with an active diameter fZ95 nm.
a 95 nm diameter. This structure can be applied to develop an electrically pumped laser with very small active-layer diameter, while maintaining a wide contact area for easy electrical connection. Details of the fabrication and structurepffiffiffiare ffi described elsewhere [12]. Also, the PQR laser’s T -dependent spectral shifts lend itself easily to large-scale integrations, and the ultra-low threshold currents permit room-temperature CW operation of high density arrays. A microscopic picture of the 16-K PQR array showing 98% yield is given in Fig. 4, corresponding to a driving current of 16 mA, or 1 mm per each PQR laser cell with fZ3 mm.
4. Conclusion We have shown that an ideal QWR nature can be realized from a toroidal micro-cavity of 3D Rayleigh–Fabry–Perot PQR modes in the peripheral region of the active MQW
λ0
Intensity (a. u.)
θv = 10°
2.0x10-9 θv = 20°
1.0x10-9
0.0 838
840
842
844
846
Wavelength (nm) Fig. 2. Multi-chromatic spectra collected at view angles qvZ10 and 208. l0 is a surface normal direction resonant mode of device.
299
Fig. 4. 16-K (128!128) PQR laser diode array.
300
O.D. Kwon et al. / Microelectronics Journal 36 (2005) 298–300
planes due to the PQCE. pffiffiffiffi Ultra-low threshold currents and QWR properties of a T -dependent spectral shifts allow us to make an H-D structure for the single PQR mode and high density PQR laser array chips.
Acknowledgements This research is supported by Samsung Co., National Research Laboratory, the BK21, and KOSEF projects of the Korean government.
References [1] E. Kapon, Quantum Well Lasers, in: P.S. Zory (Ed.), Academic, London, 1993.
[2] C. Wilmsen, H. Temkin, L.A. Coldren, Vertical-Cavity Surface Emitting Lasers, Cambridge University Press, New York, 1999. [3] A. Yariv, Appl. Phys. Lett. 53 (1988) 1033. [4] J.C. Ahn, K.S. Kwak, B.H. Park, H.Y. Kang, J.Y. Kim, O.D. Kwon, Phys. Rev. Lett. 82 (1999) 536. [5] B.H. Park, J.C. Ahn, J. Bae, J.Y. Kim, M.S. Kim, S.D. Baek, O.D. Kwon, Appl. Phys. Lett. 79 (2001) 1593. [6] S.L. McCall, A.F.J. Levi, R.E. Slusher, S.J. Pearton, A. Logan, Appl. Phys. Lett. 60 (1992) 289. [7] G. Francs, C. Girard, J. Marvig, J.C. Weeber, C. Chicane, T. David, T. Dereux, D. Peyrade, Phys. Rev. Lett. 86 (2001) 4950. [8] O.D. Kwon, M.S. Kim, B.H. Park, D.H. Park, Tech. Dig. QELS (2000); 133. [9] B.H. Park, J. Bae, M.J. Kim, O.D. Kwon, Appl. Phys. Lett. 81 (2002) 580. [10] J.W. Bae, J.W. Lee, O.D. Kwon, V.G. Minogin, Opt. Lett. 28 (2003) 1861. [11] M.K. Chin, D.Y. Chu, T. Ho, J. Appl. Phys. 75 (1994) 3302. [12] J.Y. Kim, S.J. An, J.Y. Kim, J.W. Lee, B.K. Kang, O.D. Kwon, J. Vac. Sci. Technol. B 22 (2004) 673.