Research ArticlePHYSICS

Nonvolatile infrared memory in MoS2/PbS van der Waals heterostructures

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Science Advances  20 Apr 2018:
Vol. 4, no. 4, eaap7916
DOI: 10.1126/sciadv.aap7916
  • Fig. 1 Schematic and optoelectronic transport of infrared memory device.

    (A) Schematic of infrared memory device, showing few-layer MoS2-PbS nanoplates heterostructure connected to source (S) and drain (D) electrodes. Infrared light entirely illuminates the device. (B) Band alignment of heterostructure. The photogate effect is schematically presented on the PbS side. (C) Transfer characteristic curves of Isd versus Vg under infrared illumination with variable light power density P. (D) Vg- and P-dependent photocurrent Iph extracted from transfer characteristic curves in (C). (E) Numerical simulation of carriers density (Δn) in MoS2 channel via photo injection and Vg injection. (F) Dependence of responsivity and specific detectivity on power density shows maximum R of 2.6 × 107 A/W and D* of 5.5 × 1015 Jones at P = 0.6 mW cm−2.

  • Fig. 2 PPC and rewritable memory.

    (A and B) Time evolution of Isd in MoS2-PbS heterostructure and pure MoS2, respectively. The blue dashed line labels the source-drain current under a radiation of laser pulse (Embedded Image). (C) Writing and erasing of a memory using infrared laser pulses and gate voltage pulses, respectively. A gate voltage pulse of 40 V with a duration of 100 ms is applied to reset the system. The infrared pulse power density is 0.55 mW cm−2 with a duration of 5 s. The red dashed circle indicates an instant increase of source-drain current when the gate voltage pulse is applied. a.u., arbitrary units.

  • Fig. 3 Physical principle of infrared memory and Vg pulse erasing.

    (A) Schematic illustration of time evolution of carrier distribution in MoS2-PbS heterostructure. (B) Magnitude of infrared laser pulses and Vg pulses as a function of time. The laser pulse and Vg pulse switch on at t0 and t2, respectively. (C) Change of carrier density Δn versus time in MoS2. The photogate-accumulated electron density Δnphoto in MoS2 is estimated to be 2.4 × 1024 cm−3 between t1 and t2 in device no. 3.

  • Fig. 4 Quantitative analysis of charge storage.

    (A) Schematic of electron transfer at the interface of MoS2-PbS heterostructure by tunneling or thermionic emission. Δnt shows the number of transferred electrons from MoS2 to PbS. (B) Simulated Δnt as a function of back gate Vg. (C) Quantitative analysis of Vg pulse–erased electron density Δn in MoS2. Inset shows infrared pulse– and Vg pulse–intrigued change of Isd. The ΔIp and ΔIg, respectively, represent infrared pulse–induced increase of Isd and Vg pulse–induced decrease of Isd.

  • Fig. 5 Vg pulse– and temperature-dependent optical memory.

    (A) Time evolution of Isd with a 1940-nm laser pulse–intrigued writing and Vg pulse–induced erasing. The black and red arrows indicate when the laser pulse and Vg pulse are applied, respectively. The power density of laser pulse is fixed to 5.24 mW cm−2. (B) Temperature dependence of PPC, which gradually disappears as the temperature increases to 200 from 100 K.

  • Fig. 6 Performance evaluation of infrared memory.

    (A) Charge storage stability. The infrared pulse intrigues a persistent photocurrent state. The readout current fully retains its original state even if the device is powered off for 10 min and 1 or 3 hours. The inset at the bottom of (A) shows time-dependent bias voltage Vsd for reading the states. (B) Endurance of optical writing and electrical erasing operation. The on and off states are hardly changed during the entire 2000 cycles. (C) Four states are continuously programed by multiple laser pulses with a wavelength of 1940 nm, laser pulse intensity of 27 μW cm−2, and duration of 1 s. The readout current increases with the number of laser pulses. Four resistance states are numbered as “0,” “1,” “2,” and “3.” (D) The readout charge collected for 1 s is nearly linearly dependent on the resistance states.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/4/eaap7916/DC1

    fig. S1. Chemical and structural characterization.

    fig. S2. Device morphology and optoelectronic transport.

    fig. S3. Control experiments on few-layer MoS2.

    fig. S4. Photoresponse in PbS nanoplate with an 808-nm laser illumination.

    fig. S5. The optoelectronic transport and optical memory.

    fig. S6. Photoresponse performance.

    fig. S7. Vg pulse–dependent erasing current.

    fig. S8. Optoelectronic transport and on/off ratio.

    fig. S9. Persistent photocurrent as a function of time after the laser pulse switches off.

    fig. S10. Optoelectronic transport and optical memory.

    fig. S11. Number of transferred electrons as a function of the Fermi level shift.

    table S1. Memory performance of five devices.

    note S1. Theoretical simulation of carrier injection to MoS2.

    note S2. Dynamics analysis of Vg pulse erasing.

    note S3. Roles of disorder states on the optical memory.

    note S4. Photothermal effect or Schottky barrier effect.

    References (3643)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Chemical and structural characterization.
    • fig. S2. Device morphology and optoelectronic transport.
    • fig. S3. Control experiments on few-layer MoS2.
    • fig. S4. Photoresponse in PbS nanoplate with an 808-nm laser illumination.
    • fig. S5. The optoelectronic transport and optical memory.
    • fig. S6. Photoresponse performance.
    • fig. S7. Vg pulse–dependent erasing current.
    • fig. S8. Optoelectronic transport and on/off ratio.
    • fig. S9. Persistent photocurrent as a function of time after the laser pulse switches off.
    • fig. S10. Optoelectronic transport and optical memory.
    • fig. S11. Number of transferred electrons as a function of the Fermi level shift.
    • table S1. Memory performance of five devices.
    • note S1. Theoretical simulation of carrier injection to MoS2.
    • note S2. Dynamics analysis of Vg pulse erasing.
    • note S3. Roles of disorder states on the optical memory.
    • note S4. Photothermal effect or Schottky barrier effect.
    • References (36–43)

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