Laser beam induced current microscopy and photocurrent mapping for junction characterization of infrared photodetectors

WeiCheng QIU; WeiDa HU

doi:10.1007/s11433-014-5627-6

SCIENCE CHINA Physics, Mechanics & Astronomy

SCIENCE CHINA Physics, Mechanics & Astronomy, Volume 58, Issue 2: 027001(2015) https://doi.org/10.1007/s11433-014-5627-6

Laser beam induced current microscopy and photocurrent mapping for junction characterization of infrared photodetectors

WeiCheng QIU, WeiDa HU

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ReceivedSep 1, 2014
AcceptedNov 5, 2014
PublishedDec 17, 2014

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Abstract

For non-destructive optical characterization, laser beam induced current (LBIC) microscopy has been developed into as a quantitative tool to examine individual photodiodes within a large pixel array. Two-dimensional LBIC microscopy, also generally called photocurrent mapping (PC mapping), can provide spatially resolved information about local electrical properties and p-n junction formation in photovoltaic infrared (including visible light) photodetectors from which it is possible to extract material and device parameters such as junction area, junction depth, diffusion length, leakage current position and minority carrier diffusion length etc. This paper presents a comprehensive review of research background, operating principle, fundamental issues, and applications of LBIC or PC mapping.

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State Key Program for Basic Research of China(2014CB921600)

National Natural Science Foundation of China(11322441)

Fund of Shanghai Science and Technology Foundation(14JC1406400)

References

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Figure 1
(Color online) Schematic diagram of focal plane array photovoltaic infrared detector.
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Figure 2
(Color online) The principle of a single n⁺-on-p pixel LBIC testing. Reprinted with permission from ref. [26] ? 2014, American Institute of Physics.
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Figure 3
(Color online) Two different structure frames of laser beam induced current (LBIC) test system. (a) Scanning is performed by changing position of sample under control of a two-dimensional mobile platform; (b) scanning is performed by changing the direction of the laser beam under control of a scanning galvo system.
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Figure 4
(Color online) Simulated LBIC peak-to-peak magnitudes as a function of temperature in Hg₁_- _xCd_xTe photodiodes. Reprinted with permission from ref. [30] ? 2013, ? Springer.
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Figure 5
(Color online) (a) LBIC profiles with different depths of Hg_0.69Cd_0.31Te p-n junction and (b) LBIC profiles with different lengths of Hg_0.69Cd_0.31Te p-n junction. Reprinted with permission from ref. [30] ? 2013, ? Springer.diffusion length of n-on-p HgCdTe photodiode has been investigated earlier [11,44]. In the standard diffusion length (L_p) test method, the procedure may bring about damage to the p-n junction. The test structure is also difficult to fabricate because of the need for electrical contact on the p-n junction unit as shown in Figure 6(a). In contrast, the LBIC test structure consists of only two Ohmic contacts at remote positions on either side of the device(s). The decay of the LBIC as the laser spot is scanned away from the edge of p-n junction is related to the diffusion length in p-type region. The characteristic diffusion length (L) can be obtained by fitting a simple exponential function to the LBIC curve. The exponential formula for the attenuation curve in p-type region is given by [45]
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Figure 6
(Color online) (a) The standard diffusion length (L_p) test structure (b) the standard diffusion length (L_p) test in HgCdTe photodiodes with different doping concentrations. Reprinted with permission from ref. [44] ? 2009, Chinese Physical Society.
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Figure 7
(Color online) The LBIC test for characteristic diffusion length (L) in HgCdTe photodiodes with different doping concentrations. Reprinted with permission from ref. [44] ? 2009, Chinese Physical Society.
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Figure 8
(Color online) The model structure of the p-n junction with localized junction leakage path along the horizontal portion of the junction.
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Figure 9
(Color online) The LBIC measurements are taken at a range of temperatures from 110 K to 260 K. Reprinted with permission from ref. [7] ? 2013, American Institute of Physics.
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Figure 10
(Color online) Proposed p-n junction transformation models (a) at low temperature where the typical n⁺-on-p junction is formed, (b) at moderate temperature where the n-n⁺-on-p junction is formed, and (c) at near room temperature where the n^--on-n junction are formed. Reprinted with permission from ref. [5] ? 2012, American Institute of Physics.
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Figure 11
(Color online) Temperature dependency of Hall coefficients. The R_H was positive at temperatures below 200 K (green square symbol), and negative at temperatures above 200 K (red square symbol). Reprinted with permission from ref. [26] ? 2014, American Institute of Physics.
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Figure 12
(Color online) Experimental results of temperature-dependent LBIC signal profiles with a laser power density of 1×10⁴W/cm². Reprinted with permission from ref. [5] ? 2012, American Institute of Physics.
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Figure 13
(Color online) (a) Schematic diagram of the SPCM setup. (b) SPCM image of a semiconducting CNT device D1. Left inset: Gaussian fit of one PC spot for determining the peak position and width. Right inset: physical mechanism of the contact PC generation. Reprinted with permission from ref. [50] ? 2007, American Chemical Society.
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Figure 14
(Color online) Photocurrent characterization of antenna-graphene sandwich devices. (a) Schematic illustration of a single gold heptamer sandwiched between two monolayer graphene sheets. V _G is the gate voltage. (b) Raman mapping of the as-fabricated device before (left) and after (right) deposition of the second graphene layer. (c) Photocurrent measurements show anti-symmetric photocurrent responses from the different regions of the device corresponding to specific plasmonic antenna geometries, obtained along the line scan direction. (d) Measured photocurrent for gate bias V _G between ?40 to +40 V for the heptamer antenna-patterned region 3 of the device. Reprinted with permission from ref. [70] ? 2012, American Chemical Society.
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Figure 15
(Color online) (a) Optical image of a back-gated typical graphene field effect transistor. (b) LBIC mapping at room temperature with the laser wavelength of λ = 532 nm. (c) I_photo as a function of the incident power taken at point A, B, and C with a laser wavelength of 1 μm. Reprinted with permission from ref. [71] ? 2014, Wiley-VCH.
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Figure 16
(Color online) Spatially resolved photocurrent maps at various transport regimes of a graphene device. The sequence of images displaying the n- to p-type transition, as the gate voltage is swept from 30 to -30 V. The dashed lines in the top left image indicate the position of the drain (D) and source (S) electrodes. Reprinted with permission from ref. [73] ? 2008, Nature Publishing Group.
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Figure 17
(Color online) Photovoltage map of a single layer MoS₂ FET using an excitation wavelength of 532 nm (a) and 750 nm (c). (b), (d) Photocurrent profile across the line cut in panels a, b (open blue circles). The solid red line is a Gaussian fit of the data and the arrow points at the photocurrent tail generated when the laser spot is scanned over the electrode. (e) Schematic of the photoresponse mechanism in a device dominated by photothermoelectric effect. The conduction band is drawn in blue while the valence band is drawn in red. Reprinted with permission from ref. [77] ? 2013, American Chemical Society.

The expressions of the relevant parameters in the model

Parameters	Expression
C_Rad	$\frac{1}{n_{i}^{2}} \frac{8 π}{h^{3} c^{2}} \int_{0}^{\infty} \frac{ε (E) α (E) E^{2} d E}{\exp (\frac{E}{k T}) ? 1}$
A_bbt	$? \frac{q^{2} \sqrt{2 m_{e}^{*}}}{4 π^{3} h^{2} \sqrt{E_{g}}}$
B_bbt	$\frac{n \sqrt{m_{e}^{*} / 2} E_{g}^{3 / 2}}{2 q ?}$
G_n_,_p	$\frac{Δ E_{n, p}}{k T} \int_{0}^{1} \exp (\frac{Δ E_{n, p}}{k T} u ? k_{n, p} u^{3 / 2}) d u$
K_n,p	$\frac{4}{3} \frac{\sqrt{2 m_{t} Δ E_{n, p}^{3}}}{q \frac{h}{2 π} \| E \|}$

The extracted / under different doping concentration and . Reprinted with permission from ref. ? 2009, Chinese Physical Society

N_a (10¹⁵cm^-3)	N_d (10¹⁷cm^-3)	Characteristic diffusion length L (μm)	Standard diffusion length L_p (μm)	L/Lp
1.0	1.0	8.34	7.81	1.07
4.0	1.0	6.09	5.73	1.06
8.4	1.0	5.34	4.97	1.07
8.4	5.0	5.41	5.02	1.08
8.4	1.0	5.40	5.06	1.07

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52.70.Kz	Optical (ultraviolet, visible, infrared) measurements
61.80.Ba	Ultraviolet, visible, and infrared radiation effects (including laser radiation)
85.30.De	Semiconductor-device characterization, design, and modelin

Laser beam induced current microscopy and photocurrent mapping for junction characterization of infrared photodetectors

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