Performance of the AlGaAsSb/GaInAs/GaInAs PNP and AlInAs/GaAsSb/AlInAs NPN HBTs

Interest is growing in the InP-based HBTs for high-speed complementary digital and push-pull amplifier applications. The majority of the research done on the InP-based HBTs has been concentrated on the InP/GaInAs and AlInAdGaInAs systems. In these devices, the emitter-tobase junction is generally graded to minimize the effect of large conduction band spike We report the growth and performance of AlInAs/GaAsSb/AlInAs npn HBTs and AlGaAsSb/GaInAs/GaInAs pnp HBTs lattice matched to InP substrates. In these structures all of the band-gap difference is in the valence band for AIInAdGaAsSb (0.65 eV) and conduction band for AIGaAsSb/GaInAs (1.1 eV) junctions, resulting in the large AEv (AE,) and small AE, (AE,) desirable for high performance npn (pnp) HBTs. For the first time, we have demonstrated a AlGaAsSb/GaInAs/GaInAs pnp HBT and obtained excellent microwave performance for both npn and pnp HBTs. ' The HBT structures were grown by MBE using fluxes of Sb, and As,. The epitaxial structure for the npn HBT consisted of a 500 nm n'-GaInAs subcollector, a 300 nm n-AlInAs collector, a 60 nm p'-GaAsSb base, a 2 nm InP etch stop, a 100 nm n-AlInAs emitter and followed by n'-GaInAs subcollector. The structure for the pnp HBT consisted of a 400 nm p'-GaInAs subcollector, a 400 nm P-GaInAs collector, a 60 nm n'-GaInAs, 70 nm p-A1 ,Ga,As ,,Sb 44 emitter and a 350 nm p'=-GaInAs subemitter. The GaAsSb hole mobility at a concentration of 2e19 was twice the hole mobility of GaInAs. This higher mobility will lower the base resistance and improve the performance of the GaAsSb base devices over conventional HBTs with GaInAs bases. Details of the processing of self-aligned HBTs were published in reference 1. A collector current density of 6x104 A/cm2 and an h,of 25 were measured for a 5x5 pm size npn device. We measured a BV,,, of about 1OV for the npn HBT. For the pnp HBT, a BV,,,, of 12 V, an h, of 10, and a collector current density of 2x104 A/cm2 were obtained. The high frequency performance of the HBTs in the common emitter configuration was measured with a Cascade on-wafer probe. The extrapolated f, and f,,, were 45 GHz and 34 GHz for a 5x5 pm size double heterojunction npn HBT. An f,,, of 14 GHz for a 4x6 pm pnp HBT was measured. These experimental results indicate that Sb-based npn and pnp HBTs latticematched to InP substrate are an excellent choice for complementary applications. Reference: