Optical Conductivity Enhancement Research Articles

Optical conductivity enhancement and thermal reduction of BN-codoped MgO nanosheet: Significant effects of B-N atomic interaction

We investigate the electronic, the thermal, and the optical properties of BN-codoped MgO monolayers taking into account the interaction effects between the B and the N dopant atoms. The relatively wide indirect band gap of a pure MgO nanosheet can be changed to a narrow direct band gap by tuning the B-N attractive interaction. The band gap reduction does not only enhance the optical properties, including the absorption spectra and the optical conductivity, but also the most intense peak is shifted from the Deep-UV to the visible light region. The red shifting of the absorption spectra and the optical conductivity are caused by the attractive interaction. In addition, both isotropic and anisotropic characteristics are seen in the optical properties depending on the strength of the B-N attractive interaction. The heat capacity is reduced for the BN-doped MgO monolayer, which can be referred to changes in the bond dissociation energy. The bond dissociation energy decreases as the difference in the electronegativities of the bonded atoms decreases. The lower difference in the electronegativities leads to a weaker endothermic process resulting in reduction of the heat capacity. An ab initio molecular dynamics, AIMD, calculation is utilized to check the thermodynamic stability of the pure and the BN-codoped MgO monolayers. We thus confirm that the BN-codopant atoms can be used to gain control of the properties of MgO monolayers for thermo- and opto-electronic devices.

Optical conductivity enhancement and band gap opening with silicon doped graphene

The linear optical and electronic properties of a monolayer graphene sheet are investigated using the Density Functional Theory within the Full Potential Linearized Augmented Plane Wave (FP-LAPW) formalism. Three approaches are used in this work: The Generalized Gradient Approximation (GGA), the Tran–Blaha modified Becke–Johnson exchange potential approximation (TB-mBJ); implemented in WIEN2K code; and GW (Green function G and screened Coulomb interaction W) implemented in Yambo code.The band gap of graphene with and without silicon doping and the effect of silicon on optical properties of graphene are calculated. The silicon doping opens the band gap of graphene and increases its optical conductivity. This material may be used in solar cell application. Other optical properties such as reflectivity and refractive index are also studied.

Enhancement of optical conductivity in the ultra-violet region of Cs doped ZnO sol gel thin films

Nano crystalline cesium (Cs) doped ZnO thin films were deposited on glass substrate by sol gel spin coating method with 1–3 mol.% doping concentration and different annealing temperatures. The deposited films were characterized by X-ray diffraction (XRD), Hall Effect, Photoluminescence (PL) and UV–Visible studies. XRD measurements reveal that all the samples abound in the wurtzite structure with polycrystalline nature. An increase in crystalline size from 19.60 to 44.54 nm is observed with the increase of doping concentration. Electrical conductivity of Cs doped ZnO films were observed from Hall effect measurements and the maximum carrier concentration obtained is 7.35 × 1018 cm−3. The near band emission (384 nm) peak intensity increases with the increase of Cs doping concentration and a maximum intensity 55,280 was observed for CZ3 film from PL spectrum. Also a low energy near infrared (NIR) emission peak centered at 1.62 eV appears for the Cs doped ZnO films. The average transmission of CZ film is 88 % and the absorption edge is red shifted with the increase of Cs doping concentration and also the optical conductivity increases in the UV region.

Accurate ultra‐low‐energy secondary ion mass spectrometry analysis of wide bandgap GaN/InxGa1–xN structures using optical conductivity enhancement

Ultra-low-energy secondary ion mass spectrometry has been used to undertake a structural analysis of GaN-In(x)Ga(1-x)N (x approximately 0.25) quantum wells used in optoelectronic devices. The high resistivity of intrinsic GaN-In(x)Ga(1-x)N restricts the necessary electrical path between the analyzed area and the instrument ground potential resulting in surface charge accumulation. Consequently, unstable and unrepresentative depth profiles tend to be produced. A technique known as optical conductivity enhancement (OCE) has been used during depth profiling to reduce the material resistivity. This creates an electrical path between the sample and holder, eliminating charge build up and resulting in accurate depth profiles.

Different optical conductivity enhancement (OCE) protocols to eliminate charging during ultra low energy SIMS profiling of semiconductor and semi-insulating materials

This work shows how the surface potential instabilities observed during uleSIMS profiling of various semiconductor and semi-insulating materials can be overcome by using coincident bombardment with laser light to excite electron–hole pairs. We show that the causes of the problem differ according to the material system, and may sometimes be due to the material alone, or to the interaction between the material and the primary ion beam. In some cases (e.g. Si 1− x Ge x , phosphorus implanted silicon) it is sufficient to irradiate the SIMS crater with a photon flux density above some threshold determined by the primary ion current. In others, the laser irradiation pattern must be tailored so as to create a conducting path from the crater to the sample holder.

Use of SIMS in SiGe process control

Epitaxial processes are increasingly used in semiconductor technology to cope with the requirement of ultra thin layers and ultra shallow junctions. A variety of MBE and CVD tools are used for process development and in production. Monitoring of the processed EPI-wafers is required. SIMS is a method of choice for this task. Quantifiability and even more repeatability delivered by the SIMS tool are of key importance. This paper reports the use of the FEI SIMS 4500 with a special optical conductivity enhancement (OCE) device to monitor a SiGe process in industrial routine.

Process Control of Epi-Layers for SiGe:C Hetero-Structure Bipolar Transistors

ABSTRACTThe SiGe:C hetero-structure bipolar transistor (HBT) has turned into a key technology for wireless communication. This paper describes the metrology tools for SiGe epitaxy process control. Two types of analysis are critical, (1) routine control of SiGe base and Si cap thicknesses, location and thickness of the doping layer, doping dose, Ge composition profile, and their uniformity across the wafer; and (2) root-cause analysis on non-routine problems. This is achieved by developing a transmission electron microscopy (TEM) technique allowing a thickness measurement with a reproducibility better than 3 Å. Charge-compensated low-energy secondary ion mass spectrometry (SIMS) using an optical conductivity enhancement (OCE) allows a Ge composition measurement to a required precision of 0.5 at. %.

Noise,resolution and entropy in sputter profiling

Applications of semiconductor sputter profiling in the near future will demand nm or even sub-nm depth resolution, i.e. the ability to distinguish between adjacent features in a concentration profile which are separated by 1 nm or less (not just the ability to achieve a 16-84% width of 1 nm on some edge transient). Recent developments in SIMS indicate that sputter profiling can meet this challenge—provided that instruments with high current microfocus beams less than 1 keV in energy become widely available, and data processing methods are developed to cope with the results. In this paper we discuss the nature of SIMS sputter profile data in detail and explore the consequences of noise, finite sample interval and the destruction of information by processes such as atomic mixing. The use of empirically determined response functions is discussed. We use simple arguments to show that convolution is only a valid model for atomic mixing in the low concentration limit, and contrast the use of Fourier transform and maximum entropy methods for deconvolution in these circumstances. A depth resolution of 1 nm is demonstrated without deconvolution, showing that the technique has real potential for depth resolution on the scale of 1 atomic plane.