High-performance 30-period quantum-dot infrared photodetector
Shu-Ting Chou, Shih-Yen Lin, Ru-Shang Hsiao, Jim-Yong Chi, Jyh-Shyang Wang, Meng-Chyi Wu, and Jenn-Fang Chen
Citation: Journal of Vacuum Science & Technology B 23, 1129 (2005); doi: 10.1116/1.1900730 View online: http://dx.doi.org/10.1116/1.1900730
View Table of Contents: http://scitation.aip.org/content/avs/journal/jvstb/23/3?ver=pdfcov
Published by the AVS: Science & Technology of Materials, Interfaces, and Processing
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High-performance 30-period quantum-dot infrared photodetector
Shu-Ting Chou
Department of Electrical Engineering, National Tsing Hua University, Hsinchu, Taiwan Shih-Yen Lina兲
Nanophotonics Center, Opto-Electronics and Systems Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan
Ru-Shang Hsiao
Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan Jim-Yong Chi and Jyh-Shyang Wang
Nanophotonics Center, Opto-Electronics and Systems Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan
Meng-Chyi Wu
Department of Electrical Engineering, National Tsing Hua University, Hsinchu, Taiwan Jenn-Fang Chen
Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
共Received 27 October 2004; accepted 7 March 2005; published 7 June 2005兲
In this article, quantum-dot infrared photodetectors 共QDIPs兲 with 10- and 30-period InAs/GaAs quantum-dot structures are investigated. High responsivity of 2.37 A / W and detectivity of 2.48
⫻1010cm Hz1/2/ W for 30-period QDIPs under 10 K are observed at −2.7 and 1.2 V, respectively. Almost symmetric photocurrents and dark currents under positive and negative biases are observed for both devices, which indicate a minor influence of the wetting layer on the performance of QDIPs. Lower dark current and increased photocurrent for the 30-period QDIPs would predict a better performance for devices with over a 30-period QD structure. © 2005 American Vacuum
Society. 关DOI: 10.1116/1.1900730兴
With self-assembled InAs/ GaAs quantum dots 共QDs兲 as the absorption medium, QD infrared photodetectors共QDIPs兲 have revealed its potential in the application of infrared共IR兲 detection.1–11Compared with conventional quantum-well in-frared photodetectors, normal-incident absorption, wider de-tection window, and higher-temperature operation are reported.1–7However, the influences of sample structures on the device performances are not optimized yet. In this article, the influence of InAs/ GaAs QD layer number on the perfor-mances of QDIPs is investigated. Compared with a 10-period QDIP, higher responsivity and detectivity are observed for a 30-period QDIP. Also observed is the symmetric photo- and dark currents for both devices, which implies the minor in-fluence of a wetting layer on the performances of the QDIPs. A discontinuity observed in the dark current measurement for a 30-period QDIP is attributed to the occurrence of se-quential resonant tunneling under appropriate voltage.12
The InAs/ GaAs QD samples are prepared by Riber Epineat solid-source molecular-beam epitaxy on semi-insulating GaAs substrates. 10- or 30-period 2.63 monolayer
共ML兲 InAs/30 nm GaAs QDIP samples, referred to as
De-vices A or B are sandwiched between 0.5 and 1m thick GaAs contact layers with n = 1⫻1018cm−3. The InAs QD region is n-type doped to 1⫻1018cm−3. The growth tem-perature for the InAs QDs is 495 ° C, while a higher growth temperature, 600 ° C, is adopted for the GaAs barrier layers.
After mesa formation and metal evaporation, 100
⫻100m2 devices are fabricated. The device structure is shown in Fig. 1. and the insert in the figure shows the atomic force microscopy共AFM兲 image of the InAs QDs grown un-der the same growth condition. Uniform QD distribution is observed from the AFM image. According to the AFM mea-surements, the QD density is ⬃7⫻1010cm−2. The 1
⫻1018cm−3 doping density at the InAs QD region would therefore correspond to a Si donor at each QD on average. The measurement of spectral responses is performed under an edge-coupling scheme.4–6 For this purpose, the devices are 45° polished at one side of the sample. The measurement system for spectral responses consists of a Spectral One Fou-rier transformation spectroscopy coupling with ARC
cryo-a兲Electronic mail: [email protected] Fimage of the InAs QDs grown under the same growth condition.IG. 1. Device structures of Devices A and B. The inset shows the AFM
1129 J. Vac. Sci. Technol. B 23„3…, May/Jun 2005 0734-211X/2005/23„3…/1129/3/$22.00 ©2005 American Vacuum Society 1129 Redistribution subject to AVS license or copyright; see http://scitation.aip.org/termsconditions. Download to IP: 140.113.38.11 On: Thu, 01 May 2014 03:04:25
genics and a MODEL SR570 current preamplifier. Temperature-dependent dark current-voltage characteristics are measured with a Keithley 236 source measure unit at the same ARC cryogenics.
The spectral responses measured at 10 K with different applied voltages are shown in Fig. 2. Higher peak responsiv-ity 2.37 A / W at −2.7 V is observed for Device B while De-vice A shows a peak of 0.98 A / W at −0.7 V. The photocur-rent for Device B is three times higher than that of Device A for the same electrical field. This increase indicated a non-saturated photocurrent up to a 30-period QD structure. Higher responsivity with more than a 30-period QD structure is expected. Another phenomenon observed in Fig. 2 is the symmetric photocurrents for both devices under positive and negative biases. According to a previous report,13the spectral response of a InAs/ GaAs QDIP consists of several transition mechanisms involving QD confinement states to wetting layer photoexcitation. The wetting layer-to-continuum transi-tion is not observed either under an edge-coupling scheme or normal-incident condition. And, due to the fact that the mul-tistacked QD structure is always adopted for QDIPs, the in-cident IR light has to go through multi-QD and wetting layer regions either under normal-incident or edge-coupling con-ditions. Therefore, the phenomena of symmetric phocurrents are attributed to the minor influences of the wetting layer and the three-dimensional character of the InAs QDs on the per-formance of the QDIPs.
The spectral responses of Device B under 10, 50, and 100 K at an applied voltage of 0.5 V are shown in Fig. 3. Increasing spectral responses with increasing temperature is observed, where a more pronounced increase in the wave-length range of 3 – 6m is observed. This phenomenon is attributed to the depopulation of electrons at the excited states with increasing temperature, such that the ground-to-excited state transition is increased.4 The detectivity D* is determined following the equation that detectivity D* = R共AB兲1/2/ i
n, where R, A, in, and B are the peak
responsiv-ity, device area, noise current, and measurement bandwidth, respectively. The noise current, in, could be derived through the relation in2= 4egIdB, where Idis the current under the dark environment and g is the gain assumed to be 1.3–6 The 6.2m peak detectivities for Device B at 0.5 V under 10, 50, and 100 K are 6.25⫻108, 3.82⫻107, and 2.66
⫻107cm Hz1/2/ W, respectively. Although high responsivity of 8 A / W is observed with increasing temperature up to 100 K, the peak detectivities at 6.2m decrease due to the more rapid increase of dark current with increasing tempera-ture compared with the case for photocurrent.
The dark current densities for Devices A and B under 10 K are shown in Fig. 4. The lower dark current for Device B is attributed to the increase of QD period such that the total barrier thickness is increased. Also shown in Fig. 4 is the abrupt dark current increase for Device B at ⬃1.5 and −1 V, respectively, which is attributed to the sequential
reso-FIG. 2. 10 K spectral responses of Devices A and B at +0.7 and +2.7 V,
respectively. Fvoltage 0.5 V.IG. 3. Spectral response of Device B under 10, 50, and 100 K at applied
FIG. 4. Dark current density of Devices A and B under 10 K. The inset shows the schematic diagram for the phenomenon of SRT.
1130 Chouet al.: High-performance 30-period quantum-dot infrared 1130
J. Vac. Sci. Technol. B, Vol. 23, No. 3, May/Jun 2005
nant tunneling共SRT兲 at an appropriate voltage as shown in the inset of Fig. 4.12 Since the dominant dark current com-ponent for a temperature higher than 60 K is the thermionic emission current,10,11 the activation energies under different biases can be derived through the curve fitting for the dark currents with the equation ID⬃T2e−Ea/kT, where T is
tem-perature and Ea is the activation energy which equals 共⌬Ec
− EF兲.
6 ⌬E
c is the conduction-band discontinuity and EF is
the Fermi level. The derived zero-bias activation energies are 25 and 112 meV for Devices A and B, respectively. Symmet-ric activation energies under different polarities of applied voltage are consistent with the symmetric photocurrent. Higher activation energy at zero-applied bias for Device B would indicate a lower dark current with an increasing QD layer number. Due to the higher photocurrent and lower dark current, high 6.2m detectivity of 2.48⫻1010 cm Hz1/2/ W for Device B at 10 K with responsivity 42.9 mA/ W at 1.2 V is observed. Compared with the peak detectivity 1.08
⫻109cm Hz1/2/ W with responsivity 16.4 mA/ W for Device A, Device B has⬃20 times higher peak detectivity. A higher detectivity of Device B results in a higher background-limited performance temperature of 60 K compared with 30 K for Device A.
In conclusion, symmetric photocurrents and dark currents under positive and negative biases are observed for both de-vices, which indicate a minor influence of the wetting layer and the three-dimensional character of the InAs QDs on the performance of QDIPs. And due to the increase of dark cur-rents usually being more pronounced than photocurcur-rents, the
phenomenon would result in different applied voltages for peak detectivity and peak responsivity to occur. Therefore, for a 30-period QDIP under 10 K, peak responsivity of 2.37 A / W and detectivity of 2.48⫻1010cm Hz1/2/ W are ob-served at −2.7 and 1.2 V, respectively. Lower dark current and nonsaturated photocurrent for the 30-period QDIP would indicate that better performance could be obtained for de-vices with a layer number over 30. A discontinuity observed in the dark current measurement at ⬃1.5 and −1 V for the 30-period QDIP is attributed to the occurrence of SRT.
1
J. Phillips, K. Kamath, and P. Bhattacharya, Appl. Phys. Lett. 72, 2020 共1998兲.
2
D. Pan, E. Towe, and S. Kennerly Appl. Phys. Lett. 73, 1937共1998兲.
3
S. Chakrabarti, A. D. Stiff-Roberts, P. Bhattacharya, S. Gunapala, S. Ban-dara, S. B. Rafol, and S. W. Kennerly, IEEE Photonics Technol. Lett. 16,
1361共2004兲.
4
S.-Y. Lin, Y.-R. Tsai, and S.-C. Lee, Jpn. J. Appl. Phys., Part 2 40, L1290 共2001兲.
5
S.-Y. Lin, Y.-R. Tsai, and S.-C. Lee, Appl. Phys. Lett. 83, 752共2003兲.
6
S.-Y. Lin, Y.-R. Tsai, and S.-C. Lee, Appl. Phys. Lett. 78, 2784共2001兲.
7
D. Pan, E. Towe, and S. Kennerly, Appl. Phys. Lett. 75, 2719共1999兲.
8
Z. Chen, O. Baklenov, E. T. Kim, I. Mukhametzhanov, J. Tie, A. Madhukar, Z. Ye, and J. C. Campbell, J. Appl. Phys. 89, 4558共2001兲.
9
Z. Chen, E. T. Kim, and A. Madhukar, Appl. Phys. Lett. 80, 2490共2002兲.
10
A. D. Stiff-Roberts, X. H. Su, S. Chakrabarti, and P. Bhattacharya, IEEE Photonics Technol. Lett. 16, 867共2004兲.
11
J. Y. Duboz, H. C. Liu, Z. R. Wasilewski, M. Byloss, and R. Dudek, J. Appl. Phys. 93, 1320共2003兲.
12
K. K. Choi, The Physics of Quantum Well Infrared Photodetectors共World Scientific, Singapore, 1997兲, Chap. 9.
13
H. C. Liu, M. Gao, J. McCaffrey, Z. R. Wasilewski, and S. Fafard, Appl. Phys. Lett. 78, 79共2001兲.
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JVST B - Microelectronics and Nanometer Structures
