Optical and electrical properties of undoped and doped Ge nanocrystals

Samaresh Das,Santanu Manna,Rajkumar Singha,Rakesh Aluguri,Achintya Dhar,Lorenzo Pavesi,Samit Kumar Ray

doi:10.1186/1556-276x-7-143

Samaresh Das, Santanu Manna + Show 5 more

Open Access

https://doi.org/10.1186/1556-276x-7-143

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Abstract

Size-dependent photoluminescence characteristics from Ge nanocrystals embedded in different oxide matrices have been studied to demonstrate the light emission in the visible wavelength from quantum-confined charge carriers. On the other hand, the energy transfer mechanism between Er ions and Ge nanocrystals has been exploited to exhibit the emission in the optical fiber communication wavelength range. A broad visible electroluminescence, attributed to electron hole recombination of injected carriers in Ge nanocrystals, has been achieved. Nonvolatile flash-memory devices using Ge nanocrystal floating gates with different tunneling oxides including SiO2, Al2O3, HfO2, and variable oxide thickness [VARIOT] tunnel barrier have been fabricated. An improved charge storage characteristic with enhanced retention time has been achieved for the devices using VARIOT oxide floating gate.

Highlights

The development of silicon-based optoelectronics has attracted a lot of attention over the past decade [1,2]
TEM studies of Ge nanocrystals Figure 1 shows the TEM image of Ge nanocrystals embedded in SiO2 matrix
The formation of Ge nanocrystals is attributed to the precipitation of Ge within the thermodynamically favorable SiO2 layer during post-deposition annealing in N2

Summary

Introduction

The development of silicon-based optoelectronics has attracted a lot of attention over the past decade [1,2]. Flash memory with nanocrystals floating gate has received much attention because of the high-speed write/erase operation, long retention time, and small device size [11]. A thick tunnel barrier can guarantee a long retention time of the flash-memory device, but it slows down the programming speed. Simulations and experimental results showed that a larger injected gate current density is possible for the memory devices with VARIOT structure tunnel barrier compared to memories with only a single-layered tunnel oxide [18,19]. An improved charge storage characteristic for the nanocrystal in trilayer structure is reported using high-k Al2O3 and HfO2, as compared to conventional SiO2. The experimental results showed that a VARIOT tunnel stack is attractive as a replacement for the traditional single-layer tunnel barrier for improving the data retention and programming speed simultaneously. The electrical properties of the samples were measured by a Keithley semiconductor parameter analyzer (4200-SCS, Keithley instruments, Cleveland, OH)

Results and discussions

10 K 25 K 50 K 75 K 100 K 125 K 150 K 175 K 200 K 225 K 250 K 300 K

Conclusions