Comparative studies of the epireadiness of 4in. InP substrates for molecular-beam epitaxy growth

Abstract

Four in. (100mm)-diameter semi-insulating InP substrates from multiple suppliers were evaluated and compared in terms of their epiready crystal quality and surface properties as required for growth in a multiwafer molecular-beam epitaxy system. All epiwafers in this work exhibited excellent crystalline and structural properties. The postgrowth surface morphology and defect density were typically within standard expectations; however, some fallout was observed due to variations in surface finish. Upon investigation of epilayer-substrate interfacial properties, significant differences were observed between the various vendors and also within substrate lots from individual vendors. While some substrates exhibited a clean interface, others had n-type charge accumulations of varying magnitudes. The interface contamination, silicon or sulfur arising from the substrate surface preparation process or from the substrate packaging, resulted in poor device isolation. Buffer leakage currents were proportional to the interface charge concentration and were measured in the range of 10mA∕mmto10nA∕mm. For growths of high electron mobility transistor epiwafers, the Hall transport properties were consistent for all vendors, with room temperature mobilities >10000cm2∕Vs at a channel charge of 3×1012cm−2. Similarly, the dc parameters of double heterojunction bipolar transistors grown on substrates from each vendor were nominally the same.