Temperature-Dependent DC Characteristics of InGaP∕GaAs Heterojunction Bipolar Transistors with Different Passivation

Abstract

Temperature-dependent dc characteristics of InGaP/GaAs heterojunction bipolar transistors ͑HBTs͒ without any surface passivation, with sulfur passivation, and with emitter ledge structure were systematically studied and demonstrated. Experimentally, due to the effective suppression of the thermal leakage current and hot-carrier injection around the emitter mesa edge, the device with ledge structure revealed lower base-surface recombination current density as well as better thermal stability and electrical reliability than the devices with/without sulfur passivation.Potential high-speed advantages of InGaP/GaAs npn heterojunction bipolar transistors ͑HBTs͒ have been well recognized, and significant progress in growth and fabrication has already been achieved. 1-4 However, there are some drawbacks that should be overcome to realize practical high-speed integrated circuits ͑ICs͒. One of the drawbacks is a current-gain reduction associated with the scaling down of the transistor size. 5-9 Generally, current-gain reduction in a small area mainly results from a surface recombination current and a lateral diffusion of injected carriers. [5][6][7][8][9] In order to overcome these undesired drawbacks, ͑i͒ emitter ledge structure and ͑ii͒ sulfur ͓͑NH 4 ͒ 2 S͔ chemical surface passivation have been separately employed to reduce the surface recombination current. 5-9 However, for a passivated HBT, the junction temperature could be higher than the ambient temperature due to the self-heating effect. Therefore, the issue of thermal stability is a key factor to judge HBT performance as that operated at higher temperature region.In this work, the temperature-dependent dc characteristics of InGaP/GaAs HBTs with different kinds of passivation were studied and demonstrated. Experimentally, due to the successful suppression of the thermal leakage current and hot-carrier injection around the emitter mesa edge, 10 the device with emitter ledge structure revealed lower base-surface recombination current density and better thermal stability and electrical reliability than that of other devices studied. ExperimentalThe studied HBT structure was grown by a low-pressure metallorganic chemical vapor deposition ͑LP-MOCVD͒ system on a GaAs substrate. The epitaxial layers consisted of a 5000 Å n + -GaAs ͑n + = 4 ϫ 10 18 cm −3 ͒ subcollector, a 9000 Å n − -GaAs ͑n − = 2 ϫ 10 16 cm −3 ͒ collector, a 1000 Å p + -GaAs ͑p + = 2 ϫ 10 19 cm −3 ͒ base, a 400 Å n-In 0.49 Ga 0.51 P ͑n = 3 ϫ 10 17 cm −3 ͒ emitter, a 1000 Å n + -GaAs ͑n + = 4 ϫ 10 18 cm −3 ͒ subemitter, a 500 Å n + -In x Ga 1−x As ͑x = 0 → 0.5, n + = 4 ϫ 10 18 → 2 ϫ 10 19 cm −3 ͒ graded layer, and a 500 Å n + -In 0.5 As ͑n + = 2 ϫ 10 19 cm −3 ͒ cap layer. For comparison, three different samples, denoted devices A, B, and C as shown in Fig. 1, were studied in this work. Device A was fabricated by general HBT processes including photolithography, vacuum evaporation, and chemical wet selective etching without any base-surface passivation. For device B, the sulfur ͓͑NH 4 ͒ 2 S͔ solution was us...

Parasitic Interlayer at the GaAs-on-InGaP Interface in MOVPE InGaP∕GaAs: A Study by the Chemically Sensitive (200) Diffraction

“…Several devices, such as heterojunction bipolar transistors, [1][2][3] tandem solar cells, 4,5 high electron mobility transistors 6 and lightemitting diodes, 7 are based on the lattice-matched InGaP/GaAs heterojunction because InGaP offers such advantages as large bandgap, high valence-band offset, low surface recombination velocity, reduced DX center density, low reactivity with oxygen, and good radiation hardness. However, it is difficult to grow epitaxially abrupt interfaces between InGaP and GaAs by metallorganic vapor-phase epitaxy ͑MOVPE͒ because there are no common group V atoms across the interface between the two layers.…”

Characterization of Indium Segregation in Metalorganic Vapor Phase Epitaxy-Grown InGaP by Schottky Barrier Height Measurement

“…III-V compound semiconductor devices with In-containing layers, such as InGaAs/GaAs pseudomorphic high electron mobility transistors (p-HEMTs), 1) InGaP/GaAs heterojunction bipolar transistors (InGaP-HBTs) or InGaAs/InP laser diodes (InP-LDs), [2][3][4][5] are widely used for wireless and/or optical communication systems. It is known, however, that the surface segregation of indium occurs during the growth of In-containing layers.…”