The band structure and optical gain of a new IV-group alloy GePb: A first-principles calculation

Huang, Wenqi; Cheng, Buwen; Xue, Chunlai; Yang, Hong

doi:10.1016/j.jallcom.2017.01.195

Cited by 25 publications

(11 citation statements)

References 29 publications

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“…In all four cases -having fourth-, third-, second-and first-nearest neighbour Pb atoms -the calculated value of dEg dP remains closer to that associated with the Ge fundamental (indirect) band gap, suggesting that the supercell band gap remains primarily indirect in nature, but with some direct (∼ 30 -40% Ge Γ 7c ) character, at x = 3.125%. This observation of a hybridised alloy band gap is to be compared with previous theoretical analysis of Ge 1−x Pb x alloys, which have alternatively predicted a band gap having purely indirect 28 or direct 29 character at this composition. Although our calculations show a Kramers degenerate singlet at the CB edge (cf.…”

Section: B Impact Of Pb Local Environment On Ge1−xpbx Alloy Electroni...mentioning

confidence: 58%

“…[15][16][17] Experimental confirmation of the emergence of a direct band gap in Ge 1−x Sn x -culminating in initial demonstrations of optically pumped lasing [18][19][20][21][22][23] -has stimulated broader interest in related group-IV alloys containing carbon (C) [24][25][26][27] or lead (Pb). [28][29][30] While Ge 1−x Sn x alloys have attracted significant theoretical interest, there have been few reports to date regarding Ge 1−x Pb x alloys. Initial density functional theory (DFT) calculations by Huang et al 28 predicted (i) a strong band gap reduction in response to Pb incorporation, (ii) that the indirect-to direct-gap transition occurs for Pb compositions as low as x ≈ 1%, and (iii) that the alloy band gap closes for x ≈ 2%.…”

Section: Introductionmentioning

confidence: 99%

“…More recently, the same authors presented calculations based on a more accurate GGA+U XC functional, and revised the estimated Pb composition for the transition to a direct gap to x ≈ 3.5%. 29 However, little work has yet been undertaken to analyse the nature of the indirect-to directgap transition, its consequences for the alloy electronic structure, and hence its implications for device applica-tions.…”

Section: Introductionmentioning

confidence: 99%

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First principles analysis of electronic structure evolution and the indirect- to direct-gap transition in Ge$_{1-x}$Pb$_{x}$ group-IV alloys

Broderick,

O'Halloran,

O'Reilly

2019

Preprint

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We present a theoretical analysis of electronic structure evolution in the group-IV alloy Ge1−xPbx based on density functional theory. For ordered alloy supercells we demonstrate the emergence of a singlet conduction band (CB) edge state, suggesting the emergence of a direct band gap for Pb compositions as low as x ≈ 1%. However, application of hydrostatic pressure reveals Pb-induced hybridisation, with the CB edge state in a Ge63Pb1 (x = 1.56%) supercell retaining primarily indirect (Ge L6c) character. For an ordered Ge15Pb1 (x = 6.25%) supercell we find that the CB edge has acquired primarily direct (Ge Γ7c) character, confirming the presence of an indirect-to direct-gap transition. The importance of alloy disorder in determining the details of the electronic structure is highlighted by investigating the formation of a nearest-neighbour Pb-Pb pair, which produces a large decrease (increase) in band gap (spin-orbit splitting energy) compared to equivalent structures having large Pb-Pb separation. Having established the importance of short-range disorder, we analyse the electronic structure evolution as a function of x using a series of 128-atom special quasirandom structures (SQSs). Our calculations reveal a strong reduction (increase) of the band gap (spin-orbit splitting energy), by ≈ 100 meV (≈ 40 meV) per % Pb replacing Ge. We find an indirectto direct-gap transition occurring in a narrow composition range centred about x ≈ 7%, close to which composition we calculate that the alloy becomes semimetallic. Further analysis suggests that long-range order introduced by Born von Karman (supercell) boundary conditions leads to overestimated energy splitting of the Ge L6c-derived CB states in the 128-atom SQSs. Accounting for these finite-size effects, we expect a direct band gap to emerge in Ge1−xPbx for x 3 -4%.

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Section: B Impact Of Pb Local Environment On Ge1−xpbx Alloy Electroni...mentioning

confidence: 58%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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First principles analysis of electronic structure evolution and the indirect- to direct-gap transition in Ge$_{1-x}$Pb$_{x}$ group-IV alloys

Broderick,

O'Halloran,

O'Reilly

2019

Preprint

View full text Add to dashboard Cite

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“…Among group IV alloys such conditions may be present in many systems but the electronic band structure has not been extensively analyzed. Just a handful of published theoretical and experimental papers only for selected systems [27][28][29][30][31][32][33][34][35][36][37][38][39] and no cross-sectional work can be found for such alloys. A systematic study and comparison of the group IV alloys would provide a valuable insight into the chemical trends, which this paper aims to provide and which have not been studied previously.…”

Section: Introductionmentioning

confidence: 99%

The effect of isovalent doping on the electronic band structure of group IV semiconductors

Polak¹,

Scharoch²,

Kudrawiec³

2020

J. Phys. D: Appl. Phys.

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The band gap engineering of group IV semiconductors has not been well explored theoretically and experimentally, except for SiGe. Recently, GeSn has attracted much attention due to the possibility of obtaining a direct band gap in this alloy, thereby making it suitable for light emitters. Other group IV alloys may also potentially exhibit material properties useful for device applications, expanding the space for band gap engineering in group IV. In this work the electronic band structure of all group IV semiconductor alloys is investigated. Twelve possible A:B alloys, where A is a semiconducting host (A = C, Si, and Ge) and B is an isovalent dopant (B = C, Si, Ge, Sn, and Pb), were studied in the dilute regime (0.8%) of the isovalent dopant in the entire Brillouin zone (BZ), and the chemical trends in the evolution of their electronic band structure were carefully analyzed. Density functional theory with state-of-the-art methods such as meta-GGA functionals and a spectral weight approach to band unfolding from large supercells was used to obtain dopant-related changes in the band structure, in particular the direct band gap at the Γ point and indirect band gaps at the L(X) points of the BZ. Analysis of contributions from geometry distortion and electronic interaction was also performed. Moreover, the obtained results are discussed in the context of obtaining a direct fundamental gap in Ge:B (B = C, Sn, and Pb) alloys, and intermediate band formation in C:B (B = Sn and Pb) and Ge:C. An increase in localization effects is also observed: a strong hole localization for alloys diluted with a dopant of a larger covalent radius and a strong electron localization for alloys with a dopant of smaller radius. Finally, it is shown that alloying Si and Ge with other elements from group IV is a promising way to enhance the functionality of group IV semiconductors.

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“…7,8 To date these efforts have centred on the application of tensile strain to Ge, [9][10][11][12] and on tin-(Sn-) containing Ge 1−x Sn x alloys. [13][14][15][16][17][18] Given the opportunities and challenges associated with direct-gap group-IV semiconductors, broader interest in related group-IV alloys containing lead [19][20][21][22][23] (Pb) and carbon [24][25][26][27] (C) has begun to develop.…”

Section: Introductionmentioning

confidence: 99%

Electronic structure evolution in dilute carbide Ge1−xCx alloys and implications for device applications

Broderick

Dunne

Tanner

et al. 2019

Journal of Applied Physics

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We present a theoretical analysis of electronic structure evolution in the highly-mismatched dilute carbide group-IV alloy Ge1−xCx. For ordered alloy supercells, we demonstrate that C incorporation strongly perturbs the conduction band (CB) structure by driving hybridisation of A1-symmetric linear combinations of Ge states lying close in energy to the CB edge. This leads, in the ultradilute limit, to the alloy CB edge being formed primarily of an A1-symmetric linear combination of the L-point CB edge states of the Ge host matrix semiconductor. Our calculations describe the emergence of a "quasi-direct" alloy band gap, which retains a significant admixture of indirect Ge L-point CB edge character. We then analyse the evolution of the electronic structure of realistic (large, disordered) Ge1−xCx alloy supercells for C compositions up to x = 2%. We show that short-range alloy disorder introduces a distribution of localised states at energies below the Ge CB edge, with these states acquiring minimal direct (Γ) character. Our calculations demonstrate strong intrinsic inhomogeneous energy broadening of the CB edge Bloch character, driven by hybridisation between Ge host matrix and C-related localised states. The trends identified by our calculations are markedly different to those expected based on a recently proposed interpretation of the CB structure based on the band anti-crossing model. The implications of our findings for device applications are discussed.

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The band structure and optical gain of a new IV-group alloy GePb: A first-principles calculation

Cited by 25 publications

References 29 publications

First principles analysis of electronic structure evolution and the indirect- to direct-gap transition in Ge$_{1-x}$Pb$_{x}$ group-IV alloys

First principles analysis of electronic structure evolution and the indirect- to direct-gap transition in Ge$_{1-x}$Pb$_{x}$ group-IV alloys

The effect of isovalent doping on the electronic band structure of group IV semiconductors

Electronic structure evolution in dilute carbide Ge1−xCx alloys and implications for device applications

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