Negative Photoconductivity and Memory Effects of Germanium Nanocrystals Embedded in HfO2 Dielectric

2006 ◽  
Vol 6 (1) ◽  
pp. 205-208 ◽  
Author(s):  
Shiye Wang ◽  
Weili Liu ◽  
Miao Zhang ◽  
Zhitang Song ◽  
Chenglu Lin ◽  
...  
Keyword(s):  
Forward Bias ◽  
Electron Beam Evaporation ◽  
Flat Band ◽  
Mis Structure ◽  
Negative Photoconductivity ◽  
Transmission Electron ◽  
Optimal Annealing Temperature ◽  
Tunnel Layer ◽  
Germanium Nanocrystals ◽  
Ge Nanocrystals

A metal-insulator-semiconductor (MIS) structure containing an HfO2/SiO2 stack tunnel layer, isolated Germanium (Ge) nanocrystals, and an HfO2 capping layer, was obtained by an electron-beam evaporation method. A high-resolution transmission electron microscopy (HRTEM) study revealed that uniform and pronounced Ge nanocrystals had formed after annealing. Raman spectroscopy provided evidence for the formation of Ge–Ge bonds and the optimal annealing temperature for the crystallization ratio of the Ge. The electric properties of the MIS structure were characterized by capacitance-voltage (C-V) and current–voltage (I–V) measurements at room temperature. Negative photoconductivity was observed when the structure was under a forward bias, which screened the bias voltage, resulting in a decrease in the current at a given voltage and a negative shift in flat band voltage. A relatively high stored charge density of 3.27 × 1012 cm−2 was also achieved.

Development of Ge Nanoparticles Embedded in GeO2 Matrix

2008 ◽  
Vol 8 (8) ◽  
pp. 4081-4085 ◽  
Author(s):  
Y. Batra ◽  
D. Kabiraj ◽  
D. Kanjilal
Keyword(s):  
Electron Microscopy ◽  
Annealing Temperature ◽  
Spectroscopic Studies ◽  
Electron Beam Evaporation ◽  
Granular Structure ◽  
Raman Analysis ◽  
Force Microscopy ◽  
Atomic Force ◽  
Transmission Electron ◽  
Ge Nanocrystals

Germanium (Ge) nanoparticles have attracted a lot of attention due to their excellent optical properties. In this paper, we report on the formation of Ge nanoparticles embedded in GeO2 matrix prepared by electron beam evaporation and subsequent annealing. Transmission electron microscopy (TEM) studies clearly indicate the formation of Ge nanocrystals in the films annealed at 500 °C. Fourier transform infrared (FTIR) spectroscopic studies are carried out to verify the evolution of the structure after annealingat each stage. Micro-Raman analysis also confirms the formation of Ge nanoparticles in the annealed films. Development of Ge nanoparticles is also established by photoluminescence (PL) analysis. Surface morphology study is carried out by atomic force microscopy (AFM). It shows the evolution of granular structure of the films with increasing annealing temperature.

Factors affecting Ge nanocrystal size in co-sputtered Ge+SiO2films

2000 ◽  
Vol 638 ◽  
Author(s):  
WK Choi ◽  
V Ng ◽  
YW Ho ◽  
TB Chen ◽  
V Ho
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Raman Spectroscopy ◽  
Thermal Processing ◽  
Rapid Thermal Processing ◽  
Annealing Duration ◽  
Factors Affecting ◽  
Transmission Electron ◽  
Germanium Nanocrystals ◽  
Ge Nanocrystals

AbstractThe high resolution transmission electron microscopy and Raman spectroscopy results of germanium nanocrystals embedded in SiO2 synthesized by rapid thermal processing (RTA) have been presented. From the results of samples with different Ge concentrations, it was concluded that there is a narrow window in the Ge concentration that can produce nanocrystals. We also showed that it is possible to vary RTA duration or temperature to produce Ge nanocrystals with varying sizes. Our results therefore suggest that it is possible to utilize (i) annealing duration and; (ii) temperature to tune crystal sizes for optoelectronic applications.

scholarly journals Germanium Nanocrystals Embedded in Sapphire

2005 ◽  
Vol 880 ◽  
Author(s):  
Q. Xu ◽  
I.D. Sharp ◽  
C.Y. Liao ◽  
D. O. Yi ◽  
J.W. Ager ◽  
...  
Keyword(s):  
Melting Point ◽  
Ion Beam ◽  
Implantation Dose ◽  
In Situ Tem ◽  
Transmission Electron ◽  
The Matrix ◽  
Germanium Nanocrystals ◽  
Ge Nanocrystals ◽  
Modal Size

Abstract74Ge nanocrystals are formed in a sapphire matrix by ion implantation followed by thermal annealing. Transmission electron microscopy (TEM) of as-grown samples reveals that the nanocrystals are faceted and have a bi-modal size distribution. Notably, the matrix remains crystalline despite the large implantation dose and corresponding damage. Embedded nanocrystals experience large compressive stress relative to bulk, as measured by Raman spectroscopy of the zone center optical phonon. In contrast, ion-beam-synthesized nanocrystals embedded in silica are observed to be spherical and experience considerably lower stresses. Also, in situ TEM reveals that nanocrystals embedded in sapphire melt very close to the bulk melting point (Tm= 936 °C) whereas those embedded in silica exhibit a significant melting point hysteresis around Tm.

Formation of Ge Nanocrystals in SiO2 by Electron Beam Evaporation

2008 ◽  
Vol 8 (2) ◽  
pp. 818-822 ◽  
Author(s):  
P. Basa ◽  
G. Molnár ◽  
L. Dobos ◽  
B. Pécz ◽  
L. Tóth ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Electron Beam ◽  
Sheet Resistance ◽  
Electron Beam Evaporation ◽  
Nanocrystal Size ◽  
Cross Sectional ◽  
Si Substrates ◽  
Transmission Electron ◽  
Weber Type ◽  
Ge Nanocrystals

Ge nanocrystals were formed by electron beam evaporation on SiO2 covered Si substrates. The size and distribution of the nanocrystals were studied by atomic force microscopy, scanning electron microscopy and cross-sectional transmission electron microscopy. Dependencies of the nanocrystal size, of the nanocrystal surface coverage, and sheet resistance obtained by van der Pauw method of the Ge layer have been found on the evaporation time. The suggested growth mechanism for the formation of nanocrystals is the Volmer-Weber type. The sheet resistance exhibited a power dependence on the nanocrystal size.

Wet Chemical Synthesis of Germanium Nanocrystals

2005 ◽  
Vol 879 ◽  
Author(s):  
Xianmao Lu ◽  
Brian A. Korgel ◽  
Keith P. Johnston
Keyword(s):  
Organic Contaminants ◽  
Chemical Yield ◽  
X Ray Diffraction ◽  
High Chemical ◽  
New Approach ◽  
Wet Chemical Synthesis ◽  
Transmission Electron ◽  
Germanium Nanocrystals ◽  
First Time ◽  
Ge Nanocrystals

AbstractSupercritical CO2 (sc-CO2) was first time utilized to make germanium (Ge) nanocrystals by thermolysis of diphenylgermane (DPG) or tetraethylgermane (TEG) with octanol as capping ligand at 500°C and 27.6 MPa. A new approach to prepare Ge nanocrystals of high chemical yield by reduction of GeI2 with LiAlH4 in trioctylphosphine (TOP) at 300°C is also presented. In both cases, Ge nanoparticles with high crystallinity were observed with high resolution transmission electron microscopy (HRTEM), and the presence of Ge was confirmed by X-ray diffraction (XRD) pattern. Compared to the supercritical organic solvents investigated in the previous study to make Ge nanoparticles, the reaction in sc-CO2 produced much less organic contaminants and made the removal of by-products and cleaning of the nanocrystals much easier. While Ge nanoparticles were synthesized in sc-CO2 with DPG and octanol, bulk Ge instead of nanoparticles was obtained without the presence of CO2 at the same concentration of DPG and octanol. High chemical yield of up to 75% was achieved for the Ge nanoparticles made from GeI2 with TOP, and only minimal cleaning is required to obtain Ge nanocrystals with high purity.

Characterization and Manipulation of Exposed Ge Nanocrystals

2004 ◽  
Vol 818 ◽  
Author(s):  
I.D. Sharp ◽  
Q. Xu ◽  
C.Y. Liao ◽  
D.O. Yi ◽  
J.W. Ager ◽  
...  
Keyword(s):  
Hydrofluoric Acid ◽  
Metal Films ◽  
Silica Matrix ◽  
Size Distributions ◽  
Si Substrates ◽  
Atomic Force ◽  
Transmission Electron ◽  
Oxide Matrix ◽  
Ge Nanocrystals

AbstractIsotopically pure 70Ge and 74Ge nanocrystals embedded in SiO2 thin films on Si substrates have been fabricated through ion implantation and thermal annealing. Nanocrystals were subsequently exposed using a hydrofluoric acid etching procedure to selectively remove the oxide matrix while retaining up to 69% of the implanted Ge. Comparison of transmission electron micrographs (TEM) of as-grown crystals to atomic force microscope (AFM) data of exposed crystals reveals that the nanocrystal size distribution is very nearly preserved during etching. Therefore, this process provides a new means to use AFM for rapid and straightforward determination of size distributions of nanocrystals formed in a silica matrix. Once exposed, nanocrystals may be transferred to a variety of substrates, such as conducting metal films and optically transparent insulators for further characterization.

Defects in Germanium Nanocrystals Produced by Ion Implantation

2013 ◽  
Vol 709 ◽  
pp. 148-152
Author(s):  
Yu Juan Zhang ◽  
Lei Shang
Keyword(s):  
Electron Microscopy ◽  
Light Emission ◽  
Stacking Faults ◽  
Implantation Dose ◽  
Defect Structures ◽  
High Temperature Annealing ◽  
Planar Defects ◽  
Transmission Electron ◽  
Microstructural Defects ◽  
Germanium Nanocrystals

Germanium nanocrystals (Ge-nc) were produced by the implantation of Ge+ into a SiO2 film deposited on (100) Si, followed by a high-temperature annealing. High-resolution transmission electron microscopy (HRTEM) has been used to investigate the defect structures inside the Ge-nc produced by different implantation doses (1×1016, 2×1016, 4×1016 and 8×1016 cm-2). It has been found that the planar defects such as nanotwins and stacking faults (SFs) are dominant in Ge-nc (60%) for the samples with implantation doses higher than 2×1016 cm-2, while for the sample with an implantation dose lower than 1×1016 cm-2, fewer planar defects are observed in the Ge-nc (20%). The percentages of nanotwins in the planar defects are 87%, 77%, 67% and 60% in four samples, respectively. The twinning structures include single twins, double twins and multiple twins. We also found that there are only SFs in some nanocrystals, and in others the SFs coexist with twins. These microstructural defects are expected to play an important role in the light emission from the Ge-nc.

Quantum-Well Solar Cells

MRS Bulletin ◽  
1993 ◽  
Vol 18 (10) ◽  
pp. 51-55 ◽  
Author(s):  
Keith Barnham ◽  
Jenny Barnes ◽  
Guido Haarpaintner ◽  
Jenny Nelson ◽  
Mark Paxman ◽  
...  
Keyword(s):  
Solar Cells ◽  
Solar Cell ◽  
Quantum Well ◽  
Quantum Wells ◽  
Forward Bias ◽  
Flat Band ◽  
Output Current ◽  
Novel Approach ◽  
Modulator Structure ◽  
Conventional Cell

The best present-day single-bandgap solar cells have efficiencies around 20–25%. However, the Carnot efficiency of the earth-sun system is 95%, so there is considerable potential for improvement. The fundamental efficiency limitation in a conventional solar cell results from the tradeoff between a low bandgap which maximizes light absorption and hence output current and a high bandgap which maximizes output voltage. As a result, the maximum theoretical efficiency of a conventional solar cell is around 30% in unconcentrated sunlight at a bandgap close to that of GaAs.The quantum-well solar cell is a novel approach to higher efficiency. In its simplest form, shown in Figure 1, it consists of a multiquantum-well (MQW) system in the undoped region of a p-i-n solar cell. For light with energy greater than the band-gap Eg, the quantum-well cell behaves like a conventional cell. However, light with energy below Eg can be absorbed in the quantum wells. Our studies show that if the material quality is good, the electrons and holes escape from the wells and contribute to a higher output current at a voltage between that of the barrier and well material. In AlGaAs/GaAs test devices, we have obtained efficiency enhancements of a factor of more than two when cells with quantum wells are compared with identical cells without wells.The structure in Figure 1 is, of course, essentially similar to the MQW photodiode or modulator structure that operates in reverse bias, and the quantum-well laser that operates in forward bias beyond flat band.

Ion Beam Synthesis of Luminescent SI and GE Nanocrystals in a Silicon Dioxide Matrix

1993 ◽  
Vol 316 ◽  
Author(s):  
H.A. Atwater ◽  
K.V. Shcheglov ◽  
S.S. Wong ◽  
K.J. Vahala ◽  
R.C. Flagan ◽  
...  
Keyword(s):  
Ion Beam ◽  
Optoelectronic Device ◽  
Structural Defects ◽  
Si Substrates ◽  
Localized State ◽  
Transmission Electron ◽  
Ion Beam Synthesis ◽  
Theoretical Predictions ◽  
Device Applications ◽  
Ge Nanocrystals

ABSTRACTIon beam synthesis of Si and Ge nanocrystals in an SiO2 matrix is performed by precipitation from supersaturated solid solutions created by ion implantation. Films of SiO2 on (100) Si substrates are implanted with Si and Ge at doses 1 × 1016/cm2 - 5 × 1016/cm2. Implanted samples are subsequently annealed to induce precipitation of Si and Ge nanocrystals. Raman spectroscopy and high-resolution transmission electron microscopy indicate a correlation between visible room-temperature photoluminescence and the formation of diamond cubic nanocrystals approximately 2–5 nm in diameter in annealed samples. As-implanted but unannealed samples do not exhibit luminescence. Rutherford backscattering spectra indicate a steepening of implanted Ge profiles upon annealing. Photoluminescence spectra are correlated with annealing temperatures, and compared with theoretical predictions for various possible luminescence mechanisms, such as radiative recombination of quantum-confined excitons, as well as possible localized state luminescence related to structural defects in SiO2. Potential optoelectronic device applications are also discussed.

FORMATION OF Ge NANOCRYSTALS BY ELECTRON BEAM EVAPORATION

2007 ◽  
Author(s):  
P. BASA ◽  
G. MOLNÁR ◽  
A. A. KOÓS ◽  
L. DÓZSA ◽  
Á. NEMCSICS ◽  
...  
Keyword(s):  
Electron Beam ◽  
Electron Beam Evaporation ◽  
Ge Nanocrystals
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