GaAs-based quantum dot infrared

Multi-spectral InAs/GaAs-based quantum dot infrared photoGetector with quaternary (InAlGaAs) capping operates at low bias voltage Sourav Adhikary,a Subhananda Chakrabarti,a,* Yigit Aytacb and A. G. U. Pererab

a

b

Center for Nanoelectronics, Department of Electrical Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India

Department of Physics & Astronomy, Georgia State University, Atlanta, Georgia 30303-4106, USA *Email: [email protected] ABSTRACT

The quantum dot infrared photodetector is an emerging technology for advanced imaging. Multi-color imaging technologies are favored as they extend the boundary of applications of the device. We report multi-spectral performance of MBE grown InGaAs/GaAs (device A) and InAs/GaAs (device B) based photodetector with In0.21Al0.21Ga0.58As capping at 77K. Spectral response measurement of device A shows the presence of a strong photoresponse at 10.2µm. Device B exhibits a four color response (5.7, 9.0, 14.5, 17 and 20 µm) over a broad range (520µm) at very low bias voltage. Keywords: III-V semiconductors, Photodetector, Multicolor

1. INTRODUCTION Infrared photodetector and focal plane array camera by using self-assembled quantum dot (SAQD) is an emerging technology for advanced imaging, medical research, defense etc now a days. Due to the unique property of three dimensional confinements of carriers and atom like discrete energy state, such detectors are sensitive to normal incident response, high temperature performance, longer excited state life-time and low dark current1-4. Multi-spectral imaging technologies have wide application in the field of environmental monitoring, military battle field, space science etc. There are several reports on improved QDIP performance like AlGaAs and InGaAs barrier layers in the active region5-7 ,sub monolayer (SML) QDIP structures8 and especially on multi color response as dot-in-well photodetector9, InGaAs/GaAs based QD detector10. In this letter, we report a comparative study of multi-spectral (MS) performance of MBE grown InGaAs/GaAs (device A) and InAs/GaAs (device B) based photodetector with In 0.21Al0.21Ga0.58As capping. The device A is shown long wave response 10.2-µm while an MS response is observed for sample B i.e. in the MWIR (~5.7 µm) and LWIR (~9.0, 14.5, 17 and 20 µm) regions at a very low applied bias of - 0.2 V and at 77 K.

2. EXPERIMENTS The samples were grown on a semi insulating (001) GaAs substrate by using a solid source molecular beam epitaxy (MBE) system equipped with effusion cells of Ga, In, and Al, along with an As cracker cell. The sample A deals with uncoupled InGaAs/GaAs QD heterostructure in which the dots were capped with thick combination barrier comprising 30-Å layer of quaternary In0.21Al0.21Ga0.58As and a 500-Å layer of GaAs (in fig. 1a). Both the dots and capping layer repeated for 35 periods. The other sample i.e. sample B , contains ten layers of 2.7 ML InAs QDs covered with similar combination cap of 30 Å of In0.21Al0.21Ga0.58As and 500 Å of GaAs as depicted in fig. 1 (b). Quaternary cap In0.21Al0.21Ga0.58As composition is chosen so that has a similar band-gap energy. The use of InAlGaAs cap in these structures is that it plays as a strain induced phase separation layer11. As the QDs are covered by the quaternary cap, the indium atom from the capping migrate toward the SIQD, causing Indium gradient which prevents intermixing of the QDs and the barrier material during MBE growth, which maintain shape and size of QDs.12

Quantum Dots and Nanostructures: Synthesis, Characterization, and Modeling X, edited by Kurt G. Eyink, Diana L. Huffaker, Frank Szmulowicz, Proc. of SPIE Vol. 8634, 86340V · © 2013 SPIE CCC code: 0277-786X/13/$18 · doi: 10.1117/12.2002730 Proc. of SPIE Vol. 8634 86340V-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 08/12/2014 Terms of Use: http://spiedl.org/terms

1000An -GaAs

400 Ai-GaAs 100 Ai-GaAs X 35

30A i-InAlGaAs 8 NIL InGaAs QD

2ML i-GaAS 1000Ai -GaAs

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1 µmn -GaAs

S. I. GaAs Substrate (a)

1000A n-GaAs

250A i-GaAs 250A i-GaAs 50 A i -GaAs capping

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30 A InAIGaAs quarternary capping

ALnLnLinALA 2.7 ML InAs QD 2ML i-GaAs

1000A i-GaAs

1 µm n-GaAs S. I. GaAs Substrate

(b) Figure 1 (a) – (b): Heterostructure of device A and B respectively

The device was fabricated by conventional photolithography, ICP etching and metal evaporation technique. A typical Au/Ge/Ni/Au stack was used for creating an ohmic contact. The device was subsequently annealed at 380°C for 1 min. The fabricated device was then bonded to a leadless chip carrier and mounted on the cold head of a liquid nitrogen cooled cryostat for performance measurement.

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3. RESULTS AND DISCUSSION The spectral responses were measured with a Fourier transform infrared spectrometer using a glow bar source. For Sample A, we have observed the peak at 10.2 µm 2 (a) is probably due to the bound-to-bound transition of carriers in the QDs. The spectral width (Δλ/λ) value is 0.14 for this peak (where Δλ is the FWHM of the peak). The narrow spectral width clarifies bound-to-bound transition within the QDs. Fig. 2(b) shows the spectral response of the sample B over a broad spectral range starting from the MWIR region to the LWIR region. Photoresponse peaks are observed at ~5.7, 9.0, 14.5, 17 and 20 µm. With spectral widths are ~0.07 and ~0.09 respectively, the peaks at 14.5 and 17 µm are among the narrowest compared to device A response. The peak corresponding to 5.7 µm is bound to continuum; peak at 9 µm is bound to quasi-bound transitions while the longwave responses (14-22 µm) are due to bound-to-bound transitions.

Bias=0.3 V

Spectral response (a.u.)

77 K

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Wavelength (m) (a)


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Device B 77K

Spectral response (a.u.)

Four color response

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Wavelength (m) (b) Figure 2 (a)-(b): Spectral response of the sample A and sample B respectively measured at 77K

As we are using InAs QDs for device B instead of InAs QDs which we have used for device A, the confinement probability also increases and hence the multi spectral responses are obtained as there are more excited states with in QDs. Since the photo detection range spans the entire mid-wave and long wave infrared (MWIR and LWIR) regions and the start of the far infrared (FIR) region, this detector may useful for focal plane array application.

4. CONCLUSIONS In summary, we have compared the performance of a 35-layer InGaAs/GaAs QDIP with a combined quaternary InAlGaAs and GaAs barrier capping along with QDIP consisted with InAs QDs embedded on GaAs matrix. By using thick combination capping, we designed a defect-free heterostructure. The strain induced phase separation quaternary InAlGaAs cap helps to maintain the uniform structural parameters of the QDs in the QDIP. Photo-response results showed long wave peak at 10.2 µm for device A i.e heterostructure with InGaAs QDs. Device B exhibits a broad range of photocurrent response (covering MWIR and LWIR region) ~5.7, 9.0, 14.5, 17 and 20 µm . Hence by using InAs QD and quaternary InAlGaAs layer we obtained multi spectral response operating in broad infrared window. These results are encouraging for making third generation imaging system where multicolor response is one of the key features.


ACKNOWLEDGEMENT The authors acknowledge the financial support provided by the Department of Science and Technology, India; the partial financial support provided by the Ministry of Communication and Information Technology, India, through the Centre of Excellence in Nanoelectronics.

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