HYDROSTATIC-PRESSURE DEPENDENCE OF THE ENERGY GAPS OF CDTE IN THE ZINCBLENDE AND ROCK-SALT PHASES

Recently it has been shown that CdTe has two transitions over a narrow pressure range at similar to 3.5 GPa: first zinc-blende to cinnabar a nd then cinnabar to NaCl. In the present work we report on the measure ments of the optical absorption edge of the: (i) zinc-blende CdTeI (E( g) gap, Gamma(15)(v) --> Gamma(1)(c)) phase in both increasing and dec reasing hydrostatic pressure up to 5 GPa using methanol-ethanol as the pressure transmitting medium; (ii) rocksalt CdTeIII phase using a new type of infrared diamond anvil cell from 6 to 10 GPa with argon as th e pressure medium. From the analysis of the data it has been establish ed that: (a) the E(g) gap exhibits a sublinear increase with pressure with the corresponding linear gap deformation potential being -3.8 eV; Cb) absence of any discontinuity in the direct energy gap in the pres sure range 3.5-4.2 GPa suggests that the gap of the reported CdTeII (c innabar) phase is similar to that of the zinc-blende phase; and (iii) the rocksalt CdTeIII phase is not metallic but shows a broad absorptio n edge with onset near 0.08 eV at 6.8 GPa. The blue shift of this ener gy is about 1.7 x 10(-2) eV GPa(-1).