**4. Electrical and memristor property of Mn2+doped CdSe QDs**

Huge enhancement in the conductivity of microwave-assisted doped QDs has been reported in many pieces of literature. Microwave heating enables the tuning of electrical conductivity in a desired manner by proper incorporation of dopants into the desired locations of the host material. This is evidenced by the rise in the electrical conductivity to the order of 104 for 2% Mn2+ doped CdSe over undoped one as shown in **Figure 11(a)** [17]. Here, the conduction mechanism is controlled by the electric field-assisted thermal ionization of trapped charge carriers in CdSe QDs as described in Poole–Frenkel effect as shown in **Figure 11(b)** [66]. The bandgap has no role in the conductivity and the observed colossal conductivity enhancement is solely due to the concentration of Mn2+ dopant ions.

The STM study performed on a monolayer device of Mn2+ doped CdSe QDs synthesized via microwave method founds to exhibit excellent memory characteristics as described in **Figure 12** [17]. This memristor property is evident from **Figure 12(b)** where the doped CdSe QDs switched to a high conducting state at the bias of 2.5 V. It is also observed that the device switched back to its low conducting state when the tip swept towards 3 V and the ON/OFF ratio obtained was higher than 102 . The reproducible nature of the resistive switching property over many cycles further confirms the reliability of the measurement. The threshold voltage at which the device switches to a high conducting state is found to be decreasing with an increase in the dopant concentration. Thus the notable electric bistability and the low threshold voltage of as synthesized doped CdSe QDs with the aid of simple and domestic microwave method promises its application in vivid area of future technologies which ensures minimum energy consumption per byte of the resistive data storage devices in future.

**Figure 11.**

*(a) Current–voltage characteristics of Mn-doped CdSe QDs for the samples with varying dopant concentrations. (b) Poole–Frenkel fitting for all samples with respective straight trend line [17].*

#### **Figure 12.**

*(a, b) The Tunneling current–voltage (I–V) characteristics of a monolayer of undoped and 0.2% Mn2+-doped CdSe QDs. Doped CdSe is showing low conducting state (OFF state, black line) and high conducting state (ON state, red line) for forward and backward voltage sweep direction respectively. (c, d) The differential conductance–voltage characteristics of a monolayer of undoped and 0.2% Mn2+-doped CdSe QDs respectively in their forward (black line) and backward (red line) sweep direction. The topographic images of bare Si(111). and monolayer of undoped CdSe QDs deposited on Si(111) are shown on the insets within (c) and (d) [17].*

## **5. Conclusion**

In this chapter, we mainly discussed the incorporation of impurity dopant atoms into a host semiconducting quantum dots system very efficiently using microwave heating strategy with the help of a large number of examples from the literature. It has also been observed that the zinc blend crystal phase is very efficient for the

**93**

**Author details**

Kerala, India

Sandhya K. M., Litty Thomas Manamel and Bikas C. Das\*

\*Address all correspondence to: bikas@iisertvm.ac.in

provided the original work is properly cited.

School of Physics, Indian Institute of Science Education and Research

Thiruvananthapuram (IISER TVM), Maruthamala PO, Vithura, Trivandrum,

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

*Doping of Semiconductors at Nanoscale with Microwave Heating (Overview)*

definitely reduce cost and different health and environmental hazards.

dopant incorporation than the hexagonal one. This also reflects that microwave heating can be utilized to synthesize various classes of doped zero-dimensional (0D) nanomaterials or quantum dots of many chalcogenides, oxides, carbon dots, and more with the large numbers of dopant atoms easily and more cheaply. Literature shows that the research related to two-dimensional (2D) transition metal dichalcogenides (TMDs) is booming up due to having tunable physical, electronic, and optoelectronic properties. Therefore, it would be intriguing to grow various 2D TMDs, both intrinsic and impurity-doped, via microwave heating, which will

*DOI: http://dx.doi.org/10.5772/intechopen.95558*

*Doping of Semiconductors at Nanoscale with Microwave Heating (Overview) DOI: http://dx.doi.org/10.5772/intechopen.95558*

dopant incorporation than the hexagonal one. This also reflects that microwave heating can be utilized to synthesize various classes of doped zero-dimensional (0D) nanomaterials or quantum dots of many chalcogenides, oxides, carbon dots, and more with the large numbers of dopant atoms easily and more cheaply. Literature shows that the research related to two-dimensional (2D) transition metal dichalcogenides (TMDs) is booming up due to having tunable physical, electronic, and optoelectronic properties. Therefore, it would be intriguing to grow various 2D TMDs, both intrinsic and impurity-doped, via microwave heating, which will definitely reduce cost and different health and environmental hazards.
