Effects of Al Content on Elastic Parameters of AlxGa1-xAs (0 ≤ x ≤ 1) Alloys

131-137Elastic parameters of AlxGa1-xAs (0 ≤ x ≤ 1) alloys are numerically determined and analyzed on the basis of scanning acoustic microscopy technique. Thus, the dependence of Al concentrations, x, on all features of reflection coefficient and acoustic materials signatures (critical angles of reflected modes, spatial periods, peaks of FFT spectra and their corresponding wave velocities) has been considered, analyzed and discussed. It is found that as Al content increases several behaviors are obtained: (i) all critical angles of longitudinal, transverse and Rayleigh waves, decrease, (ii) all spatial periods increase and (ii) both Rayleigh and longitudinal wave velocities increase. Moreover, the variations of these parameters, P, were quantified and semi-empirical formulas were found to be of the form: P = c + ax + bx2; from these formulas, valuable information can be derived and may be useful for AlxGa1-xAs compositional characterization

Microacoustic investigations of different structural forms of silicon

Silicon in its different structural forms is the most widely element in all modern microtechnological fields and in near future nanotechnological applications. Despite the great deal of interest in electronic, magnetic, and optical properties of all these types, only very little work is reported on their elastic properties. In this context, we determine the acoustic parameters: longitudinal, transverse and Rayleigh velocities as well as their corresponding acoustic impedances. Then, using angular spectrum model, we calculate their reflectance function and the acoustic materials signatures of these types of semiconductors. It is found that all V(z) signatures show an oscillatory behavior due to constructive and destructive interferences between different propagating surface acoustic wave modes. The values of wave velocities are found to change according to atomic arrangements as well as to defect density in different Si types. Similar variations are also noticed for their impedances as well as their elastic moduli

Effect of Passivation Layers Permittivity on DC and RF Parameters of GaN MESFETs

132-139Surface passivation impact on DC and RF characteristics of GaN MESFETs was studied using ATLAS simulator from Silvaco. It has been shown that when the relative permittivity, εr, of the inter-electrode passivation layers increases, the breakdown voltage as well as the maximum output power density increases thus improving the applications of the MESFET device in high voltage and high power. However, the high values of relative permittivity lead to an increase in the gatesource CGS and gate-drain CGD capacitances on which the radio frequency performance of GaN MESFET transistors depends strongly. In effect, this increase leads to a limitation of the performances, RF of the GaN MESFET transistors. Finally, the variations of the parameters studied as a function of εr have been quantified and mathematical expressions are established. These formulas can be very useful for the judicious choice of the passivation layer in GaN MESFETs

Elastic constants determination using the velocity of only one propagating mode: VLV_{\rm L}, VTV_{\rm T} or VRV_{\rm R}

In nondestructive micro-characterization, elastic constants are generally expressed in terms of velocities of longitudinal waves, V$_{\rm L}$, and transverse waves, V$_{\rm T}$. However, it is often difficult to determine these velocities by a single measurement. In this context, we propose the derivation of new expressions according to only one parameter: V$_{\rm L}$, V$_{\rm T}$ or Rayleigh velocity, V$_{\rm R}$. Thus, by using Viktorov formula and certain acceptable physically approximations, deduced, for any material of density $\rho$ the following relations: E = 0.757 $\rho {{\rm V}_{\rm L}}^{2}$, E = 2.586 $\rho {{\rm V}_{\rm T}}^{2}$, E = 2.99 $\rho {{\rm V}_{\rm R}}^{2}$, G = 0.293 $\rho {{\rm V}_{\rm L}}^{2}$ and G = 1.156 $\rho {{\rm V}_{\rm R}}^{2}$.The validity of these relations is put into evidence for a large number of materials (Al, Cd, Fe, Mg, Mo, Ti, W, Pt, Ni, etc) characterized by fast, medium or slow velocities. Excellent precisions of 0.007 % and 0.009 % were obtained respectively for G = f(V$_{\rm L})$ with Mo and for E = f(V$_{\rm T})$ with Fe. These very encouraging results find their applications in acoustic microscopy into which only one surface mode often dominates the acoustic materials signatures, V(z)