Journal of Crystal Growth 55 (1981) 207 212 207 North-Holland Publishing Company THE GROWTH AND CHARACTERIZATION OF METALORGANIC CHEMICAL VAPOR DEPOSITION (MO-CVD) QUANTUM WELL TRANSPORT STRUCTURES J.J. COLEMAN, P.D. DAPKUS, D.E. THOMPSON and DR. CLARKE * Rockwell International, Microelectronics Research and Development Center, Anaheim, California 92803, USA Data are presented which describe the general growth of Ga 1 ~~A1~As by metalorganic chemical vapor deposition (MO-CVD) with specific application to quantum well heterostructure (QWFI) transport structures. These data, including preliminary TEM data, Hall mobility data and carrier concentration profile data, show that alternating-layer, modulation-doped, Ga1 ~Al~As GaAs QWH samples exhibit 77 K mohiities several times greater than the observed or predicted upper limit for comparably doped bulk GaAs. The carrier concentration profile data reflect the periodic nature of the multiple layer samples but indicate an asymmetrical peak in the carrier concentration of each GaAs well. 1. Introduction metrical carrier density with a carrier concentration peak in each GaAs well. Quantum well heterostructures (QWH) of alterna- ting thin layers of GaAs and Ga1 ~A1~As have attrac- ted much attention in recent years. Since the first 2. Quantum well heterostructure growth reports [1,2] of absorption measurements on QWH structures there have been reports of various optical The growth of Ga1 ~Al~As by MO-CVD is the and electrical phenomena associated with these quasi- result of a pyrolysis reaction of the metal alkyl sour- two dimensional materials. These include laser opera- ces trimethylgallium (TMGa) and trimethylaluminum tion above the bulk GaAs band edge [3 71 and the (TMA1) with gaseous arsine. This process, which can demonstration of unusually high electron mobiities be described by the reaction equation: [7 11]. In this paper we describe the details of the growth of QWH structures by metalorganic chemical AsH3 ~x (CH3)3A1 + (1 x)(CH3)3Ga vapor deposition (MO-CVD) [7,12,13]. The MO-CVD H2 process allows the growth of uniform QWH structures -~ Ga1 ~Al~As + 3 CH4 , (1) having a large number of thin epitaxial layers [7,14] with the necessary abrupt interfaces between the is entirely a deposition process without any compet- layers [15,16]. We describe here briefly the general ing dissolution reactions. Thus, abrupt heterostruc- conditions for the MO-CVD growth of GaAs and ture interfaces in the absence of diffusion are ex- Ga1 ~Al~As and the specific conditions for the pected. Experimentally, the growth of Ga1 ~A1~As growth of a large number of thin alternating layers. takes place under conditions of excess As. The metal Data are presented, including preliminary TEM data, alkyls, which are liquids with reasonable vapor pres- temperature dependent Hall mobility data and carrier sure near room temperature, are transported to the concentration profile data, on selected QWH samples reactor by bubbled hydrogen gas. The composition of grown by MO-CVD. These samples demonstrate 77 K the epitaxial layer is determined by the relative flow mobiities several times greater than the theoretical rates (controlled electronically) of the hydrogen gas predicted upper limit for comparable bulk GaAs. The through the TMA1 (23C) and TMGa (OC) source bub- carrier concentration profile data indicate an asym- blers. A meaningful expression for this flow rate rela- tionship is given by the dimensionless flow ratio p: * Rockwell International, Science Center, Thousand Oaks, ~ — F(Al)/ [F(Al) + F(Ga)] (2) California 91360, USA. 0022-0248/81/0000 0000/502.50 © 1981 North-Holland