Low 1/f noise characteristics of AlGaAs/GaAs heterojunction bipolartransistor with electrically abrupt emitter-base junction

It is shown that the use of an electrically abrupt emitter-base junction considerably reduces the 1/f noise of self-aligned AlGaAs/GaAs heterojunction bipolar transistor (HBT). Although this device does not have depleted AlGaAs ledge passivation layer, the low-frequency noise spectra show a very low 1/f noise corner frequency of less than 10 kHz, which is much lower than previously reported value of about 100 kHz from conventional passivated or unpassivated AlGaAs/GaAs HBT's. Except for a residual generation-recombination (g-r) noise component, the noise power is comparable to that of Si BJT. It is also found that the low-frequency noise power of the AlGaAs/GaAs HBT is proportional to the extrinsic GaAs base surface recombination current square. Unlike the other HBT's reported, the noise sources associated with interface state and emitter-base (E-B) space charge region recombination are not significant for our device     

Measurement and comparison of 1/f noise and g-r noise in siliconhomojunction and III-V heterojunction bipolar transistors

This paper experimentally determines and compares the 1/f noise and the g-r noise, as components of the base noise current spectral density, in Si homojunction and III-V heterojunction bipolar transistors (HBTs) in common-emitter configuration. The noise spectra for each of these devices are obtained as functions of the base bias current (I_B), and the 1/f noise has been found to depend on I_B as I_B^γ, where γ~1.8 for the silicon BJT's and InP/InGaAs HBT's with high current gains (β~50), and γ~1.1 for the AlGaAs/GaAs HBTs with low current gains (4<β<12). The nearly constant current gain and the near square-law and inverse-square emitter area dependence of 1/f noise in silicon devices are indicative of the dominant base bulk recombination nature of this noise. The 1/f noise in the InP based HBTs has been found to be lowest among all the devices we have tested, and its origin is suggested to be the base bulk recombination as in the Si devices. For the AlGaAs/GaAs HBTs, the low current gain and the near unity value of γ, arise most likely due to the combined effects of surface, bulk, and depletion region recombinations and the base-to-emitter injection. The dependence of the 1/f noise on the base current density in the devices tested in this work, and those tested by others are compared to find out which HBT's have achieved the lowest level of 1/f noise     

Low-frequency noise in UHV/CVD epitaxial Si and SiGe bipolartransistors

In this work a comprehensive investigation of low-frequency noise in ultrahigh vacuum/chemical vapor deposition (UHV/CVD) Si and SiGe bipolar transistors is presented. The magnitude of the noise of SiGe transistors is found to be comparable to the Si devices for the identical profile, geometry, and bias. A comparison with different technologies demonstrates that the SiGe devices have excellent noise properties compared to AlGaAs/GaAs heterojunction bipolar transistors (HBT's) and conventional Si bipolar junction transistors (BJT's). Results from different bias configurations show that the 1/f base noise source is dominant in these devices. The combination of a 1/Area dependence on geometry and near quadratic dependence on base current indicates that the 1/f noise sources are homogeneously distributed over the entire emitter area and are probably located at the polysilicon-Si interface. Generation/recombination (Gm) noise and random telegraph signal (RTS) noise was observed in selected Si and SiGe devices. The bias dependence and temperature measurements suggest that these G/R centers are located in the base-emitter space charge region. The activation energies of the G/R traps participating in these noise processes were found to be within 250 meV of the conduction and valence band edges     

Analysis of the surface base current drift in GaAs HBT's

A field-induced degradation mechanism responsible for the surface base current drift in GaAs HBT's is studied on the basis of accelerated life-tests two stress conditions are applied to HBT's and associated TLM structures. An EDX analysis performed on the base ohmic contact confirms the migration of metallic species which are assessed to spread into the extrinsic base region of AlGaAs/GaAs HBT's. The self-passivated GaInP/GaAs technology is expected to improve the HBT reliability.     

Relation between low-frequency noise and long-term reliability ofsingle AlGaAs/GaAs power HBTs

Self-aligned AlGaAs/GaAs single heterojunction bipolar transistors (HBTs) were fabricated using an advanced processing technology for microwave and millimeter-wave power applications. These devices were processed simultaneously, on different epilayers with similar layer structure design supplied from different vendors. They showed similar dc characteristics (current gain, β=30) and their microwave performance was also identical (f_T=60 GHz, f_max=100 GHz). The HBTs showed different noise and reliability characteristics depending on their epilayer origin. HBT's from the high-reliability wafer showed MTTF of 10⁹ h at junction temperature of 120°C. They also presented very small 1/f noise with corner frequencies in the range of a few hundred Hz. Devices were subjected to bias and temperature stress for testing their noise and reliability characteristics. Stressed and unstressed devices showed generation-recombination noise with activation energies between 120-210 meV. Stress was found to increase the generation-recombination noise intensity but not its activation energy. These HBTs did not show any surface-related noise indicating that processing did not significantly influence noise characteristics. It was found that the base noise spectral density at low frequency can be correlated to the device long term reliability     

Tradeoff between 1/f noise and microwave performance in AlGaAs/GaAsheterojunction bipolar transistors

The 1/f noise characteristics and microwave gain of AlGaAs/GaAs heterojunction bipolar transistors (HBT's) have been investigated as a function of surface passivation ledge length. These measurements clearly demonstrate that the ledge length imposes a tradeoff between the 1/f noise and microwave power gain performance. Compared to a conventional unpassivated self-aligned HBT, HBT's with 0.4 and 1.1 μm ledge lengths improve the equivalent input base noise current spectral density at 100 Hz by as much as 2 dB and 6.5 dB, respectively; while degrading the maximum available gain at 18 GHz by 0.3 dB and 2.4 dB, respectively     

SiGe/Si HBT低频噪声特性研究

对Si/Si1-xGexHBT的低频噪声进行了模拟。频率、基极电流、集电极电流、发射极几何尺寸(面积、条长)、Ge组份x、温度等诸多因素都对低频噪声有影响。模拟结果表明,Si/SiGeHBT具有优异的低频噪声特性。     

GaAs FET's with a flicker-noise corner below 1 MHz

GaAs MESFET's with significantly reduced low-frequency noise are demonstrated through application of an understanding that the dominant noise source is generation-recombination (g-r) noise from deep level traps in the gate and backside depletion layers. A 1/f noise spectrum measured from 100 Hz to 10 MHz is modeled as the sum of Lorentzian noise spectra from a few traps subject to the temperature distribution inherent in a GaAs MESFET. The noise associated with a single mid-bandgap trapping level does not appear as an ideal Lorentzian, but rather as 1/f over nearly a decade frequency range by virtue of a time constant that is a strong function of temperature ( exp[Ea/ kT]) and an estimated temperature distribution of 22°C across the active region. The major g-r trap was characterized as having an activation energy of 0.75 eV. By reducing the g-r noise, flicker noise was decreased by more than 15 dB compared to our conventional GaAs MESFET's and the noise corner was reduced to less than 1 MHz from a typical 40 MHz. This significant reduction was achieved by using MBE layers designed to have lower trap concentrations and high channel doping. These results are within 10 dB of the estimated 1/f noise limit due to the quantum mechanics of carrier scattering [5], [14].     

On 1/f noise characteristics for 0.1 eV HgCdTe photoconductors

Sensitivities on 0.1 eV HgCdTe photoconductors with new electrode configuration and in different sizes were measured at 77K and under 10¹⁴phcm^?2s^?1 photon background conditions. After data for responsivity, generation-recombination noise (g-r noise) and minority carrier lifetime were reproduced by solving a one dimensional diffusion equation on excess minority carrier, discussions on 1/f noise were made and the following characteristics were concluded: (1) 1/f noise does not originate near electrodes for bias current. (2) 1/f noise hardly depends on sensor size and temperature in the 77–95K range, while g-r noise does. (3) 1/f noise is proportional to bias electric field, i.e. current density. (4) 1/f noise does not depend on photon background. From characteristics (2) and (4), it was concluded that 1/f noise has nothing to do with g-r noise. Finally, a new empirical formula was proposed for 1/f noise.     

Source identification and control of 1/f noise in AlGaAs/GaAs HBTsby using an on-ledge Schottky diode

Our experimental results indicate that the 1/f noise spectra density of HBTs is strongly influenced by the emitter ledge potential. By biasing an on-ledge Schottky diode, we can externally control the ledge potential and alter HBT's 1/f noise spectra density and its dependence on the base current. When biasing the on-ledge diode at V_LBE, the HBT's 1/f noise spectra densities are found to increase dramatically (up to 30 dB) from the unbiased value and exhibit stronger dependence on I_B (from I_B^1.42 to I_B^1.84). When biasing the on-ledge diode at V_L>V_BE, the 1/f noise spectra density is found to decrease (about 10 dB) and exhibit virtually no dependence on I_B (from I_B^1.42 to I_B^0.18). These findings help us identify the sources of the 1/f noise and create a novel four-terminal HBT (with an extra ledge electrode) for extremely low 1/f noise RF transceiver applications     

Low-frequency noise of InP/InGaAs heterojunction bipolartransistors

The equivalent base noise SI_b of InP/InGaAs heterojunction bipolar transistors (HBT's) with a circular pattern emitter is investigated experimentally at a low frequency ranging from 10-10⁵ Hz. The measured SI_b exhibits the 1/f dependence in an overall frequency range without any accompanying burst noise. Furthermore, SI_b varies as I_b^γ for the base current I_b and as d^-2 for the emitter diameter d, where the value of γ ranges from 1.62-1.72 depending on d of HBT's used. The 1/f noise model, which rigorously deals with the recombination current at the base surface I_bs as a function of I_b as well as of d is proposed. Applying our noise model to the dependence of SI_b on I_b, as well as on d, reveals that even though γ is less than two, the origin of SI_b is due to the recombination of electrons at the exposed base surface near the emitter edges. On the basis of theoretical considerations for the diffusion length of electrons and traps at the base surface, the Hooge parameter α_H for the noise due to the base surface recombination is deduced to be in the order of 10 ^-2 for the first time     

Generation-recombination noise in the saturation regime of MODFETstructures

Low-frequency noise measurements were performed on n-GaAs/undoped AlAs superlattice MODFET structures in the temperature and frequency ranges from 50 to 270 K and 1 Hz to 25 kHz, respectively. In both the ohmic and the velocity-saturated regime, generation-recombination (g-r) noise was dominant. Two electron traps were detected. The structure of the noise spectra in the velocity-saturated and ohmic regime were similar, but were smaller by several orders of magnitude in the latter case. For temperatures above 250 K the measurements show an additional 1/f noise at low frequencies in the velocity-saturation regime. A model that explains the g-r noise in the velocity-saturated part of the channel is proposed and applied successfully to the experimental data     

Effects of heat treatment on noise spectrum in Au-InP Schottky barriers

Measurements are reported on low frequency noise in Au-InP Schottky diodes after heating cycles. An 1/f noise component was dominant in annealing time range before 80 min. Observation of G-R noise spectra are achieved for long-term operations. Noise measurements between 77 K and 300 K have given the time constants and the activation energies of five trapping levels. The G-R processes are attributed to traps due to gold contamination in the depletion region.     

Burst and low-frequency generation-recombination noise in double-heterojunction bipolar transistors

The low-frequency noise in a double-heterojunction bipolar transistor (DHBT) consisted of burst noise and generation-recombination g-r noise. The current dependence of the base burst noise with floating collector was of the form IB³and the current dependence of the collector g-r noise with HF short circuited base was as IC^3/2. The centers involved in the noise generation had an activation energy of about 0.40 eV, with an indication of a second center of lower energy in the collector noise.     

Measurement of low-frequency base and collector current noise andcoherence in SiGe heterojunction bipolar transistors usingtransimpedance amplifiers

Transimpedance amplifiers have been used for direct study of current noise in silicon germanium (SiGe) heterojunction bipolar transistors (HBT's) at different biasing conditions. This has facilitated a wider range of resistances in the measurement circuit around the transistor than is possible when using a voltage amplifier for the same kind of measurements. The ac current amplification factor h _fe and the sum of the base and emitter series resistances (r _b+r_e) have been extracted from the noise. It has been established that the dominant noise source is situated in the base emitter junction at the emitter side and is not related to contact resistance noise. The simultaneous measurement of both the base-lead noise and the collector-lead noise and the calculation of the coherence between the signals has facilitated the pinpointing of the dominant noise source in the device and the extraction of (r_b+r_e )     

Experimental analysis and 2D simulation of AlGaAs/GaAs HBT base leakage current

Detailed experimental and modeling investigations of a field-induced degradation mechanism responsible for base leakage current drift in AlGaAs/GaAs HBT's are presented. The degradation mechanism is analyzed on the basis of the base current evolution with temperature. 2D simulation results illustrate the impact of the degradation mechanism on HBT electrical features. Calculations have been carried out on half a symmetric structure described with typical values of existing devices.     

High-f/sub max/ AlGaAs/InGaAs and AlGaAs/GaAs HBT's with p/sup +//p regrown base contacts

The present paper describes a new approach to fabricating high performance HBT's with low base resistance. Their base contact resistance is reduced by using MOMBE selective growth in the extrinsic base region-a key process in the fabrication of high-f/sub max/ AlGaAs/InGaAs and AlGaAs/GaAs HBT's. A p/sup +//p regrown base structure, which consists of a 40-nm-thick graded InGaAs strained layer and a heavily C-doped regrown contact layer, is used for the AlGaAs/InGaAs HBT's to reduce both their base transit time and base resistance, while preventing aluminum oxide incorporation at the regrowth interface. An h/sub fe/ of 93, an f/sub T/ of 102 GHz, and an f/sub max/ of 224 GHz are achieved for a 1.6-/spl mu/m/spl times/4.6-/spl mu/m HBT, together with reduced base push-out effects and improved reliability. AlGaAs/GaAs HBT's with an 80-nm-thick uniform base layer that have high f/sub max/ values ranging from 140-216 GHz are also fabricated using the selective growth technique. These results confirm the high potential of the proposed HBT's, especially for microwave and millimeter-wave applications.<>     

台面型InGaAs探测器暗电流及低频噪声研究

制备了一系列不同面积的台面型InGaAs红外探测器,通过周长面积比(P/A)的变化分析了器件的暗电流机制及低频噪声性能。结果表明,在现有的材料和工艺水平下,台面边缘和体内的产生复合电流都在总暗电流中占了较大部分。对测试结构器件的低频噪声测量表明,在反偏下,器件表现出明显的1/f噪声;由于边缘产生复合电流对小尺寸器件的影响大,其产生的噪声使得器件总噪声变大。这些结果表明,以后的工艺改进应注重减少边缘电流和体内产生复合电流。     

Measurement of the electron ionization coefficient at low electricfields in GaAs-based heterojunction bipolar transistors

Values of the electron ionization coefficient α_n in 〈100〉 GaAs extending the previously available data by two orders of magnitude, down to 1 cm^-1, are presented. The data are directly extracted from the multiplication factor, M-1, measured in lightly doped collector n-p-n AlGaAs/GaAs heterojunction bipolar transistors (HBT's). It is shown that the sensitivity of the technique is limited by the early effect, whose influence can be reduced by driving the device at constant emitter-base bias and by using heavily doped base regions. HBT's can provide simultaneously high base doping and current gain, and represent therefore an excellent tool for these measurements     

A new model for the low-frequency noise and the noise levelvariation in polysilicon emitter BJTs

Presents a new, physically-based model for the low-frequency noise in high-speed polysilicon emitter bipolar junction transistors (BJTs). Evidence of the low-frequency noise originating mainly from a superposition of generation-recombination (g-r) centers is presented. Measurements of the equivalent input noise spectral density (SIB) showed that for BJTs with large emitter areas (AE) S(I_B) is proportional to 1/f, as expected. In contrast, the noise spectrum for BJTs with submicron A_E showed a strong variation from a 1/f-dependence, due to the presence of several g-r centers. However, the average spectrum 〈S(I_B)〉 has a frequency dependence proportional to 1/f for BJTs with large as well as small A_E. The proposed model, based only on superposition of g-r centers, can predict the frequency-, current-, area-, and variation-dependency of 〈S(I_B)〉 with excellent agreement to the measured results