Investigation of the degradation of InGaAs/InP double HBTs under reverse base-collector bias stress

et al. 2007

J. Electrochem. Soc.

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...

Section: Resultsmentioning

confidence: 99%

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

Cheng

Chu

et al. 2007

J. Electrochem. Soc.

“…Previously, Wang et al demonstrated that hot electrons and holes are generated in the high electric field region in the depletion layer of the B-C junction. 25 The majority of electrons flow into the collector electrode. Some of the hot electrons close to the periphery of the B-C junctions with sufficient energy, produced by the impact ionization, may be ejected to the surface area along the periphery, which creates the surface traps.…”

Section: H138mentioning

confidence: 99%

“…Some of the hot electrons close to the periphery of the B-C junctions with sufficient energy, produced by the impact ionization, may be ejected to the surface area along the periphery, which creates the surface traps. 25 This subsequently causes an increase in leakage current. Furthermore, the hot-carrierinduced damage localized at emitter-base and B-C junction peripheries could be responsible for the increase in B-C junction leakage and decrease in current gain during bias stress.…”

Section: H138mentioning

confidence: 99%

Characteristics of an InP∕InGaAs Double Heterojunction Bipolar Transistor with an InAlGaAs∕InP Composite Collector Structure

Cheng

et al. 2008

J. Electrochem. Soc.

The characteristics of an interesting InP/InGaAs double heterojunction bipolar transistor ͑DHBT͒ with an InAlGaAs/InP composite collector structure were demonstrated and studied. Experimentally, the operation regime was wider than 11 decades in magnitude of collector current density ͑10 −6 -10 5 A/cm 2 ͒. As compared to previous reports, the studied device exhibited a relatively larger Early voltage, smaller base-collector reverse saturation current, I CBO , smaller multiplication factor, M-1, and smaller electron impact ionization, ␣. Moreover, the device studied also showed a relatively weaker temperature dependence on the electron impact ionization, ␣. Consequently, the DHBT device offers promise for low-voltage and low-power circuit applications.In recent years, heterojunction bipolar transistors ͑HBTs͒ have attracted great attention for high-speed, low-power, and microwave circuits applications. 1-4 Nevertheless, based on the high impact ionization rate in the narrow bandgap InGaAs base layer, these conventional HBTs with the InGaAs collector structure are very limited in their power applications due to the low breakdown voltage and the high output conductance. Although breakdown performance can be improved by using a wide bandgap InP layer as the collector in double HBTs ͑DHBTs͒, 5,6 the conduction band discontinuity at the base-collector ͑B-C͒ interface leads to the unwanted current blocking effect. 7 This certainly degrades the device performance. To overcome such disadvantages, several attempts have been made and reported to fabricate high-performance HBTs. These improved structures include the composite collector structure and the compositionally graded layer. 8,9 Previously, an InGaAs/InAlAs chirped superlattice of InP/InGaAs DHBTs with a continuous InAlGaAs grade layer was demonstrated by Krishnan et al. to produce the InP/InGaAs DHBTs. 10 The proposed device with thinner base ͑col-lector͒ layers showed better rf characteristics. Willen et al. used a step-graded InGaAsP collector structure in an InP/InGaAs DHBT, which exhibited good dc current gain and rf characteristics. 11 Yet, the device they studied shows a lower breakdown voltage with a greater collector thickness.In this work, an interesting InP/InGaAs DHBT with an InAlGaAs/InP composite collector structure was fabricated and studied. In this structure, the composite collector consisted of an InGaAs setback layer, a step-graded structure, and an InP layer. Moreover, the step-graded structure used a quaternary InAlGaAs material between the base and collector layers. The InAlGaAs material system had a wider tunable bandgap ͑0.75-1.46 eV͒ than the InGaAsP material system ͑0.75-1.35 eV͒. In addition, the latticematched InAlGaAs/InP material system showed a much larger valence-band offset, which is important to gain better hole confinement in the valence band. Moreover, it is known that InAlGaAs quaternary material can be employed to achieve greater material compatibility with optoelectronic devices over a 1.1-1.6 m wavelength range, such as multiqua...

“…Y. K. Fukai et al studied the reliability of submicrometer, high-speed and low-power InP HBTs with a 0.6 × 3 µm 2 emitter size at high current densities [12], and pointed out that the degradation of the B-E junction is the main factor leading to the failure of devices under high current densities. Hong Wang et al reported the reliability of InGaAs/InP DHBTs with two different emitters areas (emitter area of 5 × 20 µm 2 and 40 × 40 µm 2 ) under a high reverse B-C bias voltage (avalanche) regime [13]. The experimental studies suggest that the degradation of the device is caused by the increase in the generation-recombination centers localized at B-E and B-C junction peripheries caused by hot carriers which are generated in the reverse-bias B-C junction due to the impact ionization.…”

Section: Introductionmentioning

confidence: 99%

Characteristics and Degradation Mechanisms under High Reverse Base–Collector Bias Stress in InGaAs/InP Double HBTs

Yan,

Lu,

Cheng

et al. 2023

Micromachines

In this paper, the reliability of InP/InGaAs DHBTs under high reverse base–collector bias stress is analyzed by experiments and simulation. The DC characteristics and S parameters of the devices under different stress times were measured, and the key parameters with high field stress were also extracted to fully understand and analyze the high-field degradation mechanism of devices. The measurements indicate that the high-field stress leads to an increase in base current, an increase in base–collector (B–C) and base–emitter (B–E) junction leakage current, and a decrease in current gain, and different degrees of degradation of key parameters over stress time. The analysis reveals that the degradation caused by reverse high-field stress mainly occurs in the B–C junction, access resistance degradation, and passivation layer. The physical origins of these failure mechanisms have been studied based on TCAD simulation, and a physical model is proposed to explain the experimental results.