Research in InAs1-xPx Ternary alloy

Introduction: III-V Ternary Semiconductor alloys of InAs1-xPx are made of elements from group III and group V on the periodic table such as InAs that is commonly used to interact with Optical energy in typical optical devices.

InAs1-xPx ternary phosphates are potentially useful for Opto-electronic device applications in InAs1-xPx are a wide band-gap alloy that is often employed in red light emitting diodes (LEDs) [1, 2].

InAs1-xPx is useful material for long-wavelength surface emitting diodes Lasers [3].

Although some experimental and theoretical investigations have been reported on the band-structure Parameters for III-V InAs1-xPx crystalline phases with zinc-blend structure [4, 5] many Physical Properties of these materials remain to be determined precisely.

Today, the production and the use of InAs with technological devices with added P become more important gradually, increase more and more. Experimental studies on such type of produced semiconductor alloys are carried out intensively.

This study was carried out to shed light on the future studies of scientists who experimentally prepared and test these alloys in laboratories to help them in determining the change in amounts of additives in alloys, and to determine the accordance of theoretical studies with experiments and other theoretical works.

In the end, features of new semiconductor alloys that may be obtained by adding P to InAs structure at various ratios was examined.

In this study, electronic and optical properties of InAs1-xPxx alloys (for x= 0, 0.25, 0.50, 0.75 and 1) were calculated as a function of P composition by using Cambridge Serial Total Energy Package (CASTEP) program [6] that is based on the density functional theory (DFT) by Kohn and Sham [7].

Obtained results were found in good agreement compared with experimental and theoretical data in literature. The layout of this paper is given as followings:

The method of calculation is given in Section 2. The results and overall conclusion are presented obtained by adding P to InAs structure at various ratios was examined. In the present work, the solid sol

utions belonging to InAs1-xPxx IIII-V Ternary Semiconductor Band Energy Gap have been investigated.

Doping of P component in a Binary semiconductor like InAs and changing the composition of do pant has actually resulted in lowering of Band Energy Gap.

Thus effect of do pant increases the conductivity and decreases the Band Energy Gap and finds extensive applications. -

2. Derivation Method The electronic wave functions of InAs1-xPxx IIII-V Ternary Semiconductor were obtained by using a density-mixing minimization method for the self- consistent field (SCF) calculation, and the structures were relaxed by using the Broyden, Fletcher, Goldfarb and Shannon (BFGS) method [8].

It solves the quantum mechanical equation for the electrons within the density functional approach in the local-density approximation LDA).

For LDA, the exchange–correlation functional of Ceperley and Adler [9], as parameterized by Perdew and Zunger [10], is used.

The orbital’s of As (4s2 4p3), In (4d105s25p1), and P (3s2 3p3) are treated as valence electrons.

The tolerances for geometry optimization were set asthe difference in total energy being within 5x10-6eV/atom, the maximum ionic Hellmann-Feynman forcewithin 0.01 eV/Å, the maximum ionic displacement within 5x10-4 Å, and the maximum stress within 0.02GPa. The interactions between electrons and core ionsare simulated with separable Troullier–Martins [11] norm-conserving pseudopotentials.

A cubic unit cell is constructed with four group III atoms (As/P) and four group V atoms (P).

We have considered InAs1-xPx ternary alloys as having cubic symmetry in our calculation for all the five systems to maintain consistency and simplicity.

We expect that for x = 0.5 the alloy is a layered structure and should be non-cubic. We have taken four layers and hence a cubic unit cell for x = 0.25, 0.50, 0.75 we have replaced one, two and three As atoms, respectively, by In to get the desired concentration.

The idea of constructing an alloys by taking a large unit cell (cubic eight-atom) and repeating it three dimensionally for the calculation of the electronic structure of the semiconductor alloy has been used by Agrawal et al [17] have used an eight-atom cubic super cell to calculate the electronic properties of InAs1-xPxxalloys, although no such calculations have been performed for InAs1-xPxx ternary alloys The wave functions are expanded in the plane waves up to a kinetic- energy cutoff of 880 ev.

In this work, the k- points of 6×6×4 for x=0.5 and 4×4×4 for the other composition x, which are in the Monkhorst and Pack scheme, are used.

3. RESULTS AND DISCUSSION Electronic Properties: The band structures of the alloys show similar features to that of bulk InAs and InP. However, even accounting for the folded bands in the larger unit cell alloy systems there are important points to note.

At the top of the valence band at G, the degeneracy is broken even in the absence of spin-orbit or strain effects.

It is directly due to the presence of unequal bond lengths in the unit cell. Figure 1. Calculated band structure and DOS of InAs0.75P0.25 Table 1. Band gap energies of InAs1-xPx X=0 reference Present Theorya Theoryb Expt.c X=0.25 x=0.5 x=0.75 x=1 Present Expt d Present Expt.d Present Expt. d Present Theorya Theoryb Expt.c a Energy Bandgap (eV) 0.24 0.30 0.19 0.35 0.68 0.77 0.98 1.24 1.12 1.30 1.20 1.23 1.34 1.39

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