Optical phonons in AgGaSe₂

Abstract

Polarised infrared reflectivity measurements are made on a single crystal of the chalcopyrite compound, AgGaSe,. This is the only selenium I-111-Vr, compound so far investigated for zone centre phonon properties. They are compared with previous studies of lattice dynamics in the sulphide family and its binary zinc blende analogues. Four modes h v i n g E irreducible representation are observed between 35 and 75 pm with the light polarised perpendicular to the c-axis, while two B, modes are observed in the range 35 to 66 pm with the light polarised parallel to the o-axis. A classical dispersion harmonic oscillator computer fit is made to the data to give the oscillator parameters.An einem Einkristall der Chalkopyrit-Verbindung AgGaSe, werden polarisierte InfrarotReflexionsmessungen durchgefiihrt. Dies ist die einzige Selen-I-111-V1,-Verbindung, die bisher im Hinblick auf die Zonenzentren-Phononeneigenschaften untersucht wurde. Sie werden mit friiheren Untersuchungen der Gitterdynamik der Sulfid-Familie und den entsprechenden biniren Zinkblendekristallen verglichen. Vier Moden mit den irreduziblen Darstellungen E werden zwischen 36 und 76 pm mit senkrecht zur c-Achae polarisiertem Licht beobachtet, wiihrend zwei B,-Moden im Bereich zwischen 35 und 65 p m mit parallel zur c-Ache polarisiertem Licht gefunden werden. Es wird eine Computer-Anpassung der Dispersion eines klassischen harmonischen Oszillators an die MeDwerte durchgefiihrt, um die Oszillatorparameter anzugeben.

Origin of the low-energy mode in superionic conductors

“…58͒ are in good agreement with the observed values, and also with the values calculated from the lattice dynamics of the WZ type 58,[63][64][65]. In normal chalcopyrite compounds, the nature of phonon modes at the ⌫ point is predicted from the dispersion at ⌫ and X points in the B zone of ZB type [59][60][61][62]. A LEO phonon is observed in AgCrSe 2 ͑Refs.…”

“…[59][60][61][62] This result shows a general correlation between the LEO phonon and the long-range periodicity of crystal structure.…”

Silver Gallium Selenide (AgGaSe2) Silver Gallium Sulfide (AgGaS2)

“…They measured no and ne values in the range 0.725-13.5 ~m with four decimal figures as shown in Table I. Reflectivity measurements in the reststrahlen region have been reported by several authors [14][15][16]. Consequently, the corresponding k values are not listed in Table I. We have fitted the measured values of Boyd et al [9] to the modified Sellmeier-type dispersion formula [12] Here, the subindices o or e denote ordinary or extraordinary rays, respectively.…”

Optical absorption and photoreflectance spectroscopy of the single-crystalline chalcopyrite semiconductor AgGaSe2

“…Although the material has been the subject of many research efforts, many fundamental properties are not sufficiently evaluated or are even unknown. 9 The optical properties of AgGaSe 2 have been studied using various techniques, such as far-infrared (IR) reflectivity, 10 near-IR-ultraviolet reflectivity, [11][12][13][14][15] optical absorption, [16][17][18][19][20][21][22][23][24][25][26] photoluminescence (PL), 11,19,[27][28][29][30][31][32][33] photoconductivity, [34][35][36][37] cathodoluminescence, 38 spectroscopic ellipsometry (SE), 39 electroreflectance (ER), 16 and photoreflectance (PR). 21 Most of these studies were carried out on polycrystalline AgGaSe 2 samples.…”

“…21 Most of these studies were carried out on polycrystalline AgGaSe 2 samples. 14,[21][22][23]25,26,[28][29][30]32,34,35 Miller et al 10 grew singlecrystalline AgGaSe 2 and measured far-IR reflectivity using polarized light. PL measurements on single-crystalline AgGaSe 2 samples were performed by several authors; 28,31,33 however, polarization dependence was not taken into consideration.…”