The discovery of topological insulators (TIs) has led to numerous exciting opportunities for studying topological states of quantum physics and for exploring spintronic applications due to the new physics arising from their robust metallic surface states. Here, we report the high-quality topological insulator (BixSb1-x)2Te3 thin films using a single van der Waals GaSe buffer layer. As a result, ultra-low surface carrier density of 1.3 × 10(12) cm(-2) and a high Hall mobility of 3100 cm(2)/Vs have been achieved for (Bi0.53Sb0.47)2Te3. The high-quality films enable us to observe quantum oscillations associated with the top and bottom surface states and to manipulate the Dirac electrons and bulk holes' conduction properties. The observation of the two surface states may lead to a path towards the implementation of TIs in spintronics.