Magnetic circular dichroism of indirect excitonic transitions in GaP and In₁‐_xGa_xP

Abstract

Measurements of the magnetic circular dichroism (MCD) of the indirect absorption edge of intrinsic GaP and Inl-,Ga,P (z 2 0.77) a t temperatures from 2.5 to 300 K and at magnetic fields up to 52 kOe are reported. The fine structure of the indirect absorption edge is well resolved. The MCD peaks corresponding to LA and TA assisted indirect transitions have the same shape as the corresponding peaks in the wavelength modulated spectra, b u t the latter have different signs. That means that the thresholds of the indirect absorption edge are rigidly shifted by the magnetic field and the direction of the shift is connected with the type of the phonons. Additionally a n MCD peak appears in mixed crystals which corresponds to the no-phonon transition. It has the same sign as the LA-MCD peak. An attempt is made to interprete the experimental results by group theory within an exciton model. Further theoretical effort is necessary for a satisfactory explanation.Es wird uber Messungen des magnetischen Zirkulardichroismus (MCD) a n der indirekten Absorptionskante von undotiertem GaP und In1 _,Ga,P (z 2 0,77) bei Temperatwen zwischen 2,5 und 300 K und bei Magnetfeldern bis zu 52 kOe berichtet. Die Feiiistruktur der indirekten Absorptionskante ist gut aufgelost. Die MCD-Peaks, die LA-bzw. TAassistierten indirekten fibergiingen zuzuordnen sind, stimmen in der Form gut mit denen der entsprechenden wellenliingenmodulierten Spektren iiberein, haben jedoch im Unt,erschied zu letzteren unterschiedliche Vorzeichen. Das bedeutet, daO die Stufen in der indirekten Absorptionskante durch das magnetische Feld starr verschoben werden, daO die Richtung der Verschiebung jedoch mit der Phononenart zusammenhangt. I n Mischkristallen tritt zusiitzlich ein MCD-Peak auf, der dem No-Phonon-Ubergang entspricht und das Vorzeichen des LA-MCD-Peaks hat. Es wird ein Versuch unternommen, die experimentellen Ergebnisse mit gruppentheoretischen Mitteln innerhalb eines Exzitonenmodells zu erkliiren. Weitere theoretische Untersuchungen sind fur eine befriedigende Erkliirung notwendig.

Magneto‐Optical Investigation of the Ground State of the Indirect Free Exciton in Si and Gap

“…We estimate from k x -1.1 the hole g-value for holes bound in the exciton as = -0.3. This is in reasonable correspondence with g-values calculated from band parameters according Our interpretation can also be applied on the MCD spectra of GaP [8]. There the observable MCD lines belong partly t o other phonon types, but the signs for longitudinal and transverse phonons are the same as in Si.…”

“…For more details of the experimental results in GaP and of the experimental set-up see [S]. I n the figures in [8] a--a+ has to be replaced by a + -a-.…”

“…The group theoretical treatment is quite similar to that for Si. Our previous difficulties in interpreting the measurements in GaP in [8] arose, because we used that term splittings which result from the reduction of the double-group representation rs x As for the exciton state. The additional splitting, compared with the one used now, required a relatively strong interaction of electron and hole spin.…”

Magnetic field tunability of spin-polarized excitations in a high-temperature magnet

“…dI MCD /dE in the region near the indirect gap is especially interesting. 27 A doublet structure centered at 1.57 eV, emphasized by the black line, is clearly observed in the data taken at +10 T, whereas in the opposite (-10 T) field direction, the doublet is absent. The total splitting of this doublet in the spin down channel is 100 meV.…”