ZnGeSnN2

Contents

• Crystal Structures

• Synthesis and Growth Methods

• Electronic Properties

• X-Ray Diffraction

ZnSn_xGe_1-xN₂

ZnSn_xGe_1-xN₂ alloy with continuous variable composition and is not a mixture of different phases. Hence this materials system should allow access to the entire range of bandgap values by use of existing growth strategies.

Crystal Structure

The crystal structure may be assumed to be the same as the end compounds, i.e. Pbn2₁ except for disorder of the group IV elements on their sublattice. Additional disorder as observed in ZnSnN₂ cannot be excluded. The disorder can be modeled by means of special

quasirandom structures (SQS) [3] In ref. [3] this structure is called the "wurtizte chalcopyrite structure".

Space Group: Pbn2₁

Synthesis and Growth Methods

1. ZnSn_xGe_1-xN₂ thin films depositing on c-sapphire substrates by reactive RF cosputtering from metal targets in an argon/75% of nitrogen plasma with the chamber pressure of 3 mTorr at 270⁰ C, for x = 0 or 1. [1]

2. ZnSn_xGe_1-xN₂ alloys prepared by reactiveradio-frequency sputtering, at a base pressure of 1 × 10^-7 Torr from separate Zn, Sn, and Ge targets with 99.99+% purity, in a chamber with the composition of 1:3 argon:nitrogen gas-flow ratio at 3 mTorr pressure. [2]

Electronic Properties

The band gap in an alloy with composition A_1-xB_x is usually described by E_g(x)=(1-x) E_g(A)+x E_g(b) -b(x(1-x) with b the bowing coefficient.

Thus if the end gaps are known, it suffices to give the bowing coefficient.

Table of bowing coefficients:

Figure 2: Dependence of the bandgap of the ZnSn_1-xGe_xN₂ alloy on x, experimental data. [3]

Figure 3: Dependence of the bandgap of the ZnSn_1-xGe_xN₂ alloy on x, calculated using an SQS model and hybrid functional,

note that the end points are 1.84 eV and 3.89 eV in this calculation. [3]

Other electronic properties :

Figure 4: Resistivity at 300 K of ZnSn_xGe_1-xN₂ thin films with varying Sn concentration. The resistivity increases exponentially

with decreasing Sn content. [2]

Figure 5: Resistivity vs. temperature for samples with 5% atomic concentration of Sn[2]

Figure 6: Resistivity vs. temperature for samples with 16% atomic concentration of Sn [2]

Figure 7: Arrhenius plot (log of resistivity versus inverse temperature) for 5% at. and 16% at. samples [2]

X Ray Diffraction

X Ray diffraction and X-ray absorption fine-structure spectroscopy of ZnSn_xGe_1-xN₂ demonstrates the continuous tunability of the structure of the material and hence also the band gaps.

Figure 8: (a) X-ray diffractograms for ZnSn_xGe_1-xN₂ samples on Sapphire with different compositions[1]

(b)XRD θ -2θ for films with various compositions grown on c -plane GaN template substrates. [3]

Figure 9: X-ray diffractograms for ZnSn_xGe_1-xN₂ samples with

different compositions(2θ vs x) [1]

The shifting of the 2θ position of the (002) peak with changing composition which exhibits the quality of no phase separation in the process of alloying. The X-ray diffraction results are showing that the band gap of ZnSn_xGe_1-xN₂ alloy can potentially be varied over a wide range as a function of the composition.

References.

[1]. Naomi C. Coronel at al, Photovoltaic Specialists Conference (PVSC), 2012 38th IEEE (2012).

[2]. Amanda M. Shing at al, APL Materials 102,(2015).

[3]. Narang, P at al. (2014), Bandgap Tunability in Zn(Sn,Ge)N₂ Semiconductor Alloys. Adv. Mater., 26: 1235–1241.

[4] Atchara Punya and Walter R. L. Lambrecht, Materials Science Foruum Vols. 717-720, (2012), pp 1331-1334