* Corresponding author. Tel.: #1-212-854-1580; fax: #1- 212-854-7081. E-mail address: ik29@columbia.edu (I. Kuskovsky). Journal of Crystal Growth 214/215 (2000) 335}339 Photoluminescence characterization of MBE grown Zn  Be  Se I. Kuskovsky*, C. Tian, C. Sudbrack, G.F. Neumark, S.P. Guo, M.C. Tamargo School of Mines and Department of Applied Physics, Columbia University, New York, NY 10027, USA Center for Advanced Technology on Ultrafast Photonic Materials and Applications, Center for Analysis of Structures and Interfaces (CASI), Department of Chemistry, City College-CUNY, New York, NY 10031, USA Abstract We report photoluminescence (PL) studies of high-quality Zn  Be  Se "lms grown by molecular beam epitaxy (MBE) on GaAs substrates by use of a novel growth method of Be}Zn co-irradiation before the growth of a thin ZnSe bu!er layer. Samples show double-crystal X-ray linewidth as narrow as 23 arcsec. Low-temperature (13 K) PL of undoped samples showed free exciton emission, which de"ned the bandgap and showed that this system gives bandgap bowing. In addition, there was dominant deep bound excitonic recombination. We also suggest that deep PL can be caused by low structural quality of "lms, rather than by speci"c impurity states. Nitrogen-doped samples (with net acceptor concentra- tions up to 210 cm) show strong impurity related photoluminescence.  2000 Elsevier Science B.V. All rights reserved. PACS: 78.55.!m; 78.55.Et; 81.5.Hi Keywords: II}VI compound semiconductors; ZnBeSe; MBE; Photoluminescence; Excitons 1. Introduction Wide bandgap semiconductors are of high inter- est for fabricating devices emitting light in the green, blue, and UV spectral regions. However, performance of such devices depends on the ad- equacy of bipolar doping of the materials and on device `lifetimea. It is well known that good p-type doping is still a problem for most II}VI wide ban- dgap semiconductors. The best devices have been fabricated lattice matched to a GaAs substrate, with ZnMgSSe as a cladding layer and ZnSSe as a guiding layer [1]. However, during molecular beam epitaxial (MBE) growth, the sulfur sticking coe$cient depends strongly on the substrate tem- perature, making it extremely di$cult to avoid compositional #uctuations [2]. Recently, the use of Be instead of sulfur in ZnSe-based alloys (i.e. Zn  Be  Se ternary alloy) has been suggested [3]. This also increases the hardness of the material [4], which is important for improved device lifetime, 0022-0248/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 0 2 4 8 ( 0 0 ) 0 0 1 0 8 - 1