Question

Hobbis et al (Inorg. Chem., 2019, 58 (3), pp 1826–1833) thoroughly examined the properties of a niobium-iron-antimony semiconductor material. Although their reported synthetic procedure was a fairly straightforward stoichiometric melting and subsequent crystallization of the pure elements, they did not observe the predicted behavior of an intrinsic semiconductor. Instead, their compound was found to exhibit characteristics of a very lightly n-doped semiconductor instead. They hypothesize that this is due to the formation of so-called “antiphase domains” during crystallization, where the local pattern of atoms in small regions in the solid is the exact reverse of the rest of the crystal structure. Given the three elements involved, suggest an explanation (using a diagram if you find it helpful) for how this change in atomic pattern gives rise to n-type doping behavior.

Answer 1

According to my knowledge this must be the answer . The required graphs and conclusions that are drawn are in the form of images.

• Charge doping in a semiconductor is takento originate the presence of dopants, elements that are not present in the original compound effectively adds and subtracts charge from the dispersive component of electronic structure that yields n type and p type doping. In another way there is a type of charge doping through defects called antisite defects thsat can also lead to such type of doping that can originate from antiphase boundaries.
• Let us construct cells of dimensions (units of fcc lattice)2*1*1,4*1*1,6*1*1,8*1*1,12*1*1,16*1*1 & 24*1*1 and computed the electronic structure. In each of these cells an antiphase boundary(APB) , a plane mirror symmetry not present in the original cell, but has been placed in the centre of cell. The Fe sublattice is located away from the APB .

• For a 4*1*1 NbFeSb supercell ,where the APB is indicated in a green plane.By extending the cell dimensions to long distances in order to isolate APB energy , the formation energy of various APB with supercell can be calculated as

E= ( (E_tot)^APB - (E_tot)^bulk ) / (2*A)

(E_tot)^APB - the total energy of supercell contains an APB

(E_tot)^bulk - total energy of an equivallent supercell representing a ideal bulk crystal without APB

A - the cross-sectional area in (b*c)

and the factor 2 arises due to phase boundary structure of periodic boundary conditions.

• The calculated APB formation is nearly independent of this spacing,but by changing only a few percent from 2*1*1 cell to the 24*1*1 cell , which has this spacing more than 70 armstrong. This suggests that our calculations were accurate capture for APB energy (large spacing).
• Evaluating the effect of APB on electronic structure , the densities of bulk NbFeSb were calculated and they show a band gap of 0.5 eV with 0.4eV estimated value of resistivity. Then, the fermi level is observed to move into the highly dispersive conduction band because of the lack of dopants per sec.
• Graph states this curves :

• Conclusions that are drawn :