104 Journal of Crystal Growth 80(1987) 104-112 North-Holland, Amsterdam CLASSIFICATION AND ORIGINS OF GaAs OVAL DEFECTS GROWN BY MOLECULAR BEAM EPITAXY K. FUJIWARA, K. KANAMOTO, Y.N. OHTA, Y. TOKUDA and T. NAKAYAMA Central Research Laboratory, Mitsubishi Electric Corporation, Amagasaki, Hyogo 661, Japan Received 29 July 1986; manuscript received in final form 24 September 1986 By extensive surface and cross sectional microscopic observations, oval defects on single GaAs and multiple GaAs/A1GaA5 epilayers grown by molecular beam epitaxy (MBE) were investigated. It is found that there are at least seven different representative kinds of oval defects which possess distinct morphological characteristics. Among six different types of oval defects without macroscopic core particulates, four types are ascribed to surface microscopic contaminations, while other two types to the Ga source material. However, the majority of oval defects with our MBE system were usually the type with macroscopic core particulates and were found to originate at the epilayer/substrate interface. They are, therefore, attributed to surface macroscopic contaminations. 1. Introduction variations by many reasons, we consider it very important that we should classify the oval defects Molecular beam epitaxy (MBE) has currently and then investigate the trends when discussing been used as a powerful tool to study compound the causes of the oval defects. semiconductor physics and devices which utilized In this paper, we classified the oval defects by hyper-abrupt heterointerfaces and doping profiles extensive surface and cross sectional microscopic [1]. However, the macroscopic surface defects [2—5] observations. Based on the observations for a often observed on epilayers grown by MBE with a number of GaAs and A1GaAs epilayers grown density of 102_105 cm 2 have been a troublesome under different conditions, occurrence, shape, size problem for practical applications such as in- and density were examined in details for each tegrated circuits. To overcome this problem, the types of oval defects, and their possible origins origins of such morphological defects were in- were identified and discussed. In section 2, the vestigated by a number of researchers [2—20]. experimental details of the MBE growth and mi- Several studies have indicated that the most corn- croscopic observations are described. In section 3, mon type is the ovally shaped defect, so called results and discussion are presented, divided into “oval defect”. The orientation of the long-axis is three subsections: (1) classification of oval de- parallel to the (110) direction. Experimentally the fects, (2) oval defects originating from substrate defect formation was related to the substrate pre- preparations, (3) oval defects originating from ex- parations [5—11],the Ga source cell (Ga spitting cess gallium. Finally the conclusion is given in [3,12] and Ga oxides [4,13—15])and the As source section 4. cell [7,16]. However, it is recently found that the factors causing the main oval defects are not unique but several depending on the system em- 2. Experimental ployed (hardware) and on the growth conditions used (software) [11,16,20]. There are, in fact, van- For oval defect evaluation, single GaAs epi- ous kinds of oval defects, and their density ap- layers with thicknesses of 1 j~mand 5 ~im and pears to vary greatly in a complex way with the multiple A1GaAs (2.2 im)/A1As(0.5 ~sm)/ experimental conditions. Because of the density GaAs(0.9 ~m)/A1As(0.2 ~sm)/ GaAs(1.7 p.m)/ 0022-0248/87/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)