200 GHz max f , τ f InP/In 0.53 Ga 0.47 As/InP Metamorphic Double Heterojunction Bipolar Transistors on GaAs Substrates Y.M. Kim, M. Urteaga, M. Dahlstrom, M.J.W. Rodwell, A.C. Gossard Department of Electrical and Computer Engineering University of California, Santa Barbara, CA 93106, USA E-mail : kymdow@ece.ucsb.edu Abstract InP/In 0.53 Ga 0.47 As/InP Double Heterojunction Bipolar Transistors were grown on GaAs substrates using a high- thermal-conductivity InP metamorphic buffer layer. InP metamorphic buffer was selected because it has a large thermal conductivity, which is very important in high power device operation. 200 GHz max f and 200 GHz τ f were obtained. This max f is the highest reported for a metamorphic HBT. The breakdown voltage BV CEO was 6 V and the DC current gain β was 27. The base-collector reverse leakage current was 54 nA at V CB =0.3V. I. Introduction Double heterojunction bipolar transistors [1,2,3] (DHBTs) have applications in high frequency communications and radar. HBTs using InGaAs or GaAsSb epitaxial base layers and InGaAs or InP epitaxial collector layers -- lattice- matched to InP -- currently exhibit significantly higher current-gain and power-gain cutoff frequencies than GaAs- based HBTs. However, InP substrates are expensive and are available only in smaller diameters than GaAs substrates. Additionally, 100-mm-diameter InP substrates are fragile and are readily broken during semiconductor manufacturing. This has motivated the investigation of metamorphic growth of InP- based DHBTs on GaAs substrates [4]. As reported earlier [5,6,7], the buffer layer thermal conductivity has a large impact upon the device thermal resistance, especially for high speed applications where power densities must be high in order to minimize C∆V/I charging times. We therefore use InP metamorphic buffer layers. We had earlier reported MHBTs with 207 GHz τ f & 140 GHz max f [5]. We here report metamorphic HBTs (MHBTs) with greatly improved max f resulting from improved base Ohmic contacts. 200 GHz max f and 200 GHz τ f were obtained. In this work, Pd (30Å)/ Ti (200Å)/ Pd (200Å) / Au (400Å) base Ohmic contacts were used. These provide specific contact resistance well below 10 -6 Ω cm 2 . The base-collector leakage current was found to be 54 nA at V CB =0.3V. Though this leakage is higher than the 2 nA cbo I for lattice matched DHBTs in our laboratory, it is still acceptable for most circuit applications. II. Growth InP/In 0.53 Ga 0.47 As/InP DHBTs were grown on GaAs substrate using a Varian Gen II MBE system equipped with a valved phosphorous (P) cracker cell and a valved arsenic (As) Table 1 The sample structure of MHBT Layer Material Doping (cm -3 ) Thickness (Å) Emitter Cap In0.53Ga0.47As 2 × 10 19 : Si 300 Grade In0.53Ga0.47As/In0.52Al0.48A s 2 × 10 19 : Si 200 N + Emitter InP 1 × 10 19 : Si 700 N - Emitter InP 8 × 10 17 : Si 500 Grade In0.53Ga0.47As/In0.52Al0.48A s 4 × 10 17 : Si 280 Base In0.53Ga0.47As 4 × 10 19 : Be 300 Set back In0.53Ga0.47As 2 × 10 16 : Si 300 Grade In0.53Ga0.47As/In0.52Al0.48A s 2 × 10 16 : Si 240 Delta Doping InP 3.6 × 10 18 : Si 30 Collector InP 2× 10 16 : Si 1430 Sub collector In0.53Ga0.47As 1× 10 19 : Si 250 Sub collector InP 1× 10 19 : Si 1250 Buffer InP undoped 15000 GaAs (100) semi-insulating substrate