J. Phys. Chew. So/ iris Vol. 56. No. 3/ 4. pp. 415-418. 1995 Copyright c, 1995 Elsevier Science Ltd Pnnted in Great Britain. All rights reserved 0022.3697195 $9.50 + 0.00 THE EFFECT OF PRESSURE ON THE LUMINESCENCE OF CdTe/CdMnTe QUANTUM WELLS P. PERLIN,1_ S. SHILO,? T. SOSIN,1_ Y. TYAGUR,I_ T. SUSK1.t W. TRZECIAKOWSKI,~ G. KARCZEWSKI,~ T. WOJTOWICZ,~ E. JANIK,f A. ZAKRZEWSKI,$ M. KUTROWSKIS and J. KOSSUTZ tHigh Pressure Research Center, Polish Academy of Sciences, Sokolowska 29, 01-142 Warsaw, Poland IInstitute of Physics. Polish Academy of Sciences, Aleja Lotnik6w 32/46, 02-668 Warsaw, Poland Abstract-We have studied photoluminescence in two CdTe/Cd, _ ,Mn,Te multiple quantum-well samples with well thicknesses from 9.7 A to IO0 A and with barrier com~sitions s = 0.5 and .Y = 0.68. The following effects have been observed after hydrostatic pressure up to 3 GPa was applied: (i) decrease of the luminescence intensity from wider wells, which can be related to the stress-induced deterioration of initially strained CdTe layers; (ii) transfer of photoexcited electrons from thinner wells into the barriers where Mn-related recombination occurs; (iii) large negative pressure coefficient (4 -80 meV/GPa) of the Mn-related photoluminescence; and (iv) positive pressure coefficients for CdTe well luminescence, which do not practically depend on the well thickness, while their magnitude decreases with increasing Mn concentration in the barriers (75 meV/GPa for Cd,,Mn,, Te and 60 meV/GPa for Cd,, 3z Mn, ,Te). Ke~xxv&: A. semiconductors, A. quantum wells, C. high pressure, D. luminescence. 1. INTRODUCTION 2. EXPERIMENTAL CdMnTe is the most extensively studied semi- conductor of the A”MnBV’ family [l]. Cd, _.,Mn,Te crystallizes in the zinc blende structure up to compositions of x =0.7. At about 3GPa the structural phase transition to rocksalt structure occurs. The optical energy gap, E,, exhibits an anomaly as a function of X. For x < 0.35, Ea increases with increasing X, while for x > 0.35 [2] the localized state related to Mn and situated below the conduction band minimum causes a stabilization of E,. The sign of the pressure coefficient of the gap changes at this critical compo- sition from about +75 meV/GPa for x < 0.35 to - 50 meV/GPa, for s > 0.35 131. In [4] the critical composition was found to be between 0.4 and 0.6, and for .Y= 0.6 the pressure coefficient of the lu- minescence was determined as -60 meV/GPa. It is still unclear if the Mn-related transition in absorption and in luminescence is an intra-atomic impurity-like transition within the Mn 3d’ manifold or an inter- band transition between the Te 5p states (valence band) and the Mn 3d states [5]. High pressure experiments were performed in a diamond anvil cell (Merrill-Bassett design). Standard methanol~thanol4: 1 mixture was used as a pressure transmitting medium. The diamond anvil cell was placed in a continuous-flow Oxford Instruments cryostat. Pressure was changed at room temperature. It was calibrated by measuring the position of the absorption edge of the GaAs substrate. Since the pressure ~riation of the GaAs energy gap is well known, we estimate the accuracy of pressure determi- nation to be better than +O.Ol GPa. We excited the luminescence by the 50mW blue-green light of an argon laser. The purpose of this work was to study how these unusual features of CdMnTe affect the properties of quantum-well structures of CdTe/CdMnTe. Two samples of CdTe/CdMnTe were grown on a (100) GaAs substrate in the EPI 620 MBE system. Sample 1 (growth number 09233A) had the following buffer layers: ZnTe (0.2 pm), CdTe (0.8 itm) and Cd,,zMn,,,Te (2 pm). Then. the 100 A, 60 A, 40 A, and 2OA CdTe quantum wells separated by the 500 A barriers of Cd,,?Mn,,,,Te were grown, Finally, the Cd,, I~Mnlt,hKTe cap layer of 1000 $, was deposited. Sample 2 (growth number 02084) had the following buffer layer: CdTejZnTe superlattice. 3.5 itrn of CdTc, and 500 A of Cd,,,Mn,,,Te. Then, eight quantum wells were deposited starting from 24 monolayers (78 A) and finishing with three 415