Correlation between Photoreflectance Spectra and Electrical Characteristics of InP/GaAsSb Double Heterojunction Bipolar
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B6.2.1
Correlation between Photoreflectance Spectra and Electrical Characteristics of InP/GaAsSb Double Heterojunction Bipolar Transistors Hiroki Sugiyama1, Yasuhiro Oda1, Haruki Yokoyama1, and Takashi Kobayashi1 Masahiro Uchida2 and Noriyuki Watanabe2, 1 NTT Photonics Laboratories, NTT Corporation, 2NTT Advanced Technology Corporation 1,2 3-1, Morinosato Wakamiya, Atsugi-shi, Kanagawa 243-0198, Japan ABSTRACT We report a photoreflectance (PR) characterization of InP/GaAsSb double-heterojunction bipolar transistor (DHBT) epitaxial wafers grown by metal-organic vapor-phase epitaxy (MOVPE). The origin of the Franz-Keldysh oscillations (FKOs) in the PR spectra was identified by step etching of the samples. FKOs from the InP emitter region were observed in the wafer with low recombination forward current at the emitter-base (E/B) heterojunction. In contrast, they did not appear when recombination current was dominant. The absence of the FKOs from the emitter indicates the high concentration of the recombination centers at the E/B heterojunction. We have also measured PR spectra from InAlP/GaAsSb/InP DHBT wafers. Pronounced FKOs from InAlP emitter reflect the suppression of recombination at E/B heterojunctions. INTRODUCTION InP/GaAsSb double-heterojunction bipolar transistors (DHBTs) have recently attracted much attention. One advantage of these DHBTs is that the type-II (staggered) band alignment of their heterostructure eliminates any possible current blocking effect at the base-collector junction, and electrons are injected ballistically from the GaAsSb base to the InP collector [1,2]. Another advantage is that hydrogen passivation of carbon atoms is significantly suppressed in a GaAsSb base grown by metal-organic vapor-phase epitaxy (MOVPE) [1,3,4] For device manufacturing, MOVPE-grown carbon-doped GaAsSb bases are much more favorable than MOVPE-grown carbon-doped InGaAs bases because the latter requires postgrowth annealing for dopant activation [5]. As these InP/GaAsSb DHBTs move from research to the production phase, nondestructive diagnosis of the quality of epitaxial layers becomes important for cost reduction. Recently, photoreflectance (PR) spectroscopy has been accepted as a useful method for the room-temperature nondestructive characterization of HBT wafers because built-in electric fields in the heterojunction can be determined by analyzing Franz-Keldysh oscillations (FKOs) in spectra [6,7]. In addition, the PR method is sensitive to recombination centers in regions with a large potential slope even at room temperature [8,9], and useful for the diagnosis of crystal quality of heterojunctions in InP/InGaAs HBTs [10,11]. In spite of such advantages, there have been few PR studies of InP/GaAsSb DHBT wafers [12].
B6.2.2
In this report, we present a PR study of InP/GaAsSb DHBT wafers and discuss the correlation between the PR spectra and electrical characteristics of the emitter-base (E/B) heterojunctions in the DHBTs. We found that FKOs from the emitter are related to the amount of recombination current at
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