Pergamon J. Phys. Chem. Solids Vol. 56, No. 3/4. pp. 349-352. 1995 Ekvier Science Ltd Printed in Great Britain 0022-3697/95 $9.50 + 0.34 HIGH PRESSURE DETERMINATION OF AlGaInP BAND STRUCTURE A. D. PRINS, J. L. SLY, A. T. MENEY, D. J. DUNSTAN, E. P. O’REILLY, A. R. ADAMS zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIH and A. VALSTERT Physics Department, University of Surrey, Guildford, Surrey GU2 SXH, U.K. tPhilips Optoelectronics Centre, P.O. Box 80000, 5600 J A, Eindhoven, The Netherlands Abstract-Low temperature photoluminescence measurements have been carried out at hydrostatic pressures up to 80 kbar to determine the band structure of the disordered (Al,Ga, _ Y)osIn,,P alloy system. Using a series of specifically designed samples we have measured how the r, L and X conduction band energies vary with strain and aluminium content. The direct band gap varies linearly from that of GaInP at a rate of 0.61x eV. The position of the X minimum in GainP is found to be 280meV above the I-, increasing linearly with aluminium content at a rate of 0.085x eV. Measurements of unstrained and I % compressively strained GaInP put lower limits on the l--L, separation of 125 meV and 175 meV, respectively. Ke~~ards: A. ~m~conductors, C. high pressure, D. electronic structure, D. luminescence. 1. INTRODUCTION AlGaInP is currently attracting considerable interest in the field of optoelectronics, in particular for the manufacture of visible lasers [I, 21. By varying the alloy composition and using the effects of strain it is possible to produce devices emitting in the 6X&690 nm wavelength range. Successful design and analysis of such structures requires accurate knowl- edge of the positions of the conduction band F, L and X minima. However, values quoted in the literature for the indirect band gaps have varied considerably and as a result the design and optimisation of laser structures from this alloy system has so far depended on these uncertain band gaps together with valence band energies calculated using model solid theory [3]. Some of the uncertainty arises from variations in ordering on the Group 111 sub-lattice. The pressure coefficients of the conduction band of these alloys are about + 8, +4 and -2 meV/kbar for the F, L and X points, respectively (the exact values depend on the alloy composition and the degree of ordering). Using hydrostatic pressure it is possible to alter their relative positions, eventually making the band structure indirect. Extrapolation of photolu- minescence (PL) energy data above crossover allows us to determine with spectroscopic accuracy the positions of indirect minima at ambient pressure. In this paper we report on the results of such experiments in which we determine how the F and X conduction band energies vary as functions of strain and aluminium content in the disordered (Al,Ga, _ Y)0,51n0,,P alloy system and put limits on the positions of the L minima. 2. EXPERIMENTAL TECHNIQUE Six samples were studied under hydrostatic press- ure. All were grown by metal-organic-vapour-phase epitaxy (MOVPE) on (001) oriented GaAs substrates under conditions optimized for good quality disor- dered growth [4]. Four of the samples were bulk (Al,Ga, _ r)0.51n0,,P layers, each approximately I pm thick, with aluminium contents of x = 0, 0.3,0.4 and 0.7, respectively. Double crystal X-ray diffraction of the GaInP (x = 0) layer showed its lattice mismatch to be less than 0.1%. PL linewidths for the direct band gap samples were between 6 meV and 14 meV at 2 K. These samples were used for high pressure PL experiments to determine the composition depen- dence of the f’ and X band gap energies. The two remaining samples consisted of 1% compressively strained Gao:IxIn,,,zP quantum wells (with well widths of 23 and 100 A, respectively) in unstrained Ga,,In,,,P barriers. PL linewidths of the quantum wells were measured at 2 K to be IO meV. These samples were grown in order to determine the pos- ition of the L minimum. The results of rapid thermal annealing experiments have verified these bulk layers and structures to be highly disordered [5]. 349