FZU 7.11.2006 1

Mn-doped Ga(As,P) and (Al,Ga)As ferromagnetic semiconductors

J.Mašek, J. Kudrnovský, F.Máca, T.Jungwirth,Jairo Sinova, A.H.MacDonald

FZU 7.11.2006 2

Outline

• Motivation• Enhanced Curie temperature in mixed hosts• Defects: substitutional vs. interstitial Mn in the

Ga(As,P) and (Al,Ga)As• Summary

FZU 7.11.2006 3

Motivation

• Wider bandgap than in GaAs Mn d- states closer to the valence band edge

• Mn acceptor level deeper in VB and more localized extend of exchange coupling

• Smaller lattice constant of GaP enhanced p-d hybridization

FZU 7.11.2006 4

III-V family: Internal reference rule

FZU 7.11.2006 5

Lattice constant: Vegard’s law

FZU 7.11.2006 6

Tight-binding model

FZU 7.11.2006 7

Tight-binding model – cont.

FZU 7.11.2006 8

Tight-binding model – cont.

FZU 7.11.2006 9

TC: LDA+U calculationsmean-field calculations for 5% and 10% Mn

FZU 7.11.2006 10

Range of exchange coupling

FZU 7.11.2006 11

Mn interstitials: formation energies

• Formation energies Es,i (xs,xi) of MnGa and MnI as functions of partial concentrations xs and xi .

• Balanced state: Es(xs,xi) = Ei(xs,xi) .

FZU 7.11.2006 12

Ga(As,P): MnGa vs MnI

FZU 7.11.2006 13

(Al,Ga)As: MnGa , MnAl vs. MnI

FZU 7.11.2006 14

Substitutional vs.interstitial Mn

FZU 7.11.2006 15

Summary

• Strength of p-d hybridization is more important for TC high than band structure effect

• The range of exchange coupling in (Ga,Mn)(As,P) unchanged for less than 50% P

• Suppressed formation of MnI in (Ga,Mn)(As,P)

• Remarkable increase of TC in (Ga,Mn)(As,P)

• No improvement expected in (Al,Ga,Mn)As

• Preferential formation of MnI in (Al,Ga)As