Low-noise properties of dry gate recess etched InP HEMTs

Lattice-matched InAlAs-InGaAs HEMTs with dry etched and wet etched gate recesses have been fabricated and both high-frequency and noise measurements have been carried out. The highly selective dry etching process ensures uniform device parameters. The small signal and noise performance shows only minor differences between the two transistor types. There is no evidence of detrimental effects caused by dry etching that reduce the electrical and noise performance of the device at high frequencies. These results show that dry etched InP HEMT's have suitable characteristics for the fabrication of MM-wave integrated circuits     

Analytical bias dependent noise model for InP HEMT's

A practical device model for both high frequency small signal and noise behavior of InP-HEMT's depending on both gate and drain voltage has been developed. The model is based on the two-piece linear approximation using charge control and saturation velocity models. Combining large signal model and analytical expressions for the noise source parameter P, R, and C, an analytical bias-dependent noise model can be obtained. For implementation into high frequency simulation software, the exact calculated bias dependence was mathematically fitted by elementary functions. It could be shown that lowest noise is observed when the drain current for maximum gain is reduced to a third while the drain voltage is reduced to the start of the saturation region V_ds =0.6 V. Modeling scaling effects of the noise behavior shows that lowest noise is observed for a gate width of 1×40 μm. Multi-finger layouts are preferable for gate widths above 70 μm. Furthermore it is shown, that the optimum width of each finger decreases with the number of fingers     

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     

Hydrogen-induced piezoelectric effects in InP HEMT's

In this letter, we have investigated hydrogen degradation of InP HEMT's with Ti/Pt/Au gates. We have found that V_T shifts negative after exposure to hydrogen, and exhibits an L_G and orientation dependence. We postulate that ΔV_T is at least in part due to the piezoelectric effect. Hydrogen exposure leads to the formation of TiH_x, producing compressive stress in the gate. This stress induces a piezoelectric charge distribution in the semiconductor that shifts the threshold voltage. We have independently confirmed TiH_x formation under our experimental conditions through Auger measurements. Separate radius-of-curvature measurements have also independently confirmed that Ti/Pt films become compressively stressed relative to their initial state after H₂ exposure     

Highly uniform N-InAlAs/InGaAs HEMT's on a 3-in InP substrate usingphotochemical selective dry recess etching

Large-area photochemical selective dry etching has been developed for use in InGaAs/InAlAs heterojunction fabrication involving CH₃ Br gas and a low-pressure mercury lamp. The etch rate of the InGaAs layer was 17 nm/min and the etch ratio of InGaAs to InAlAs was around 25 to 1. The dry recess was performed for N-InAlAs/InGaAs HEMT's on a 3-in wafer using photochemical etching. The standard deviation of the threshold voltage across the wafer was 18 mV at a threshold voltage of -0.95 V, and the transconductance of 456 mS/mm was obtained for a 1.1-μm-long gate within a standard deviation of 14.9 mS/mm     

Reliability testing of InP HEMT's using electrical stress methods

In this paper, we discuss the results of three different electrical stress tests on InP-based HEMT's and their implications toward reliability. These are hot electron (HE) stress, transmission line pulse (TLP) measurements, and RF overdrive stress. Some processing parameters have been varied to investigate their influence on reliability issues. HE stress is performed on a set of Si₃N ₄ passivated devices with increasing recess width. Degradation is observed to be largely dependent on recess width, due to changes at the InAlAs-Si₃N₄ interface. With TLP measurements, an ESD-like reliability study is performed on devices with different types of Schottky barriers. Although epilayers with In_0.40Al_0.00 as Schottky material show improved breakdown and leakage characteristics over In_0.52Al_0.48 As, pulsed stress tests reveal an earlier breakdown. Finally, the degradation under large-signal RF overdrive stress is determined with a nonlinear network measurement system (NNMS). Both on- and off-state degradation are studied with this set-up. Results appeared to be strongly dependent on the phase difference between the stress voltage waves applied at the device ports     

Low-frequency noise properties of dynamic-threshold (DT) MOSFET's

This paper shows that MOSFET operated in dynamic-threshold (DT) mode (V_body=V_gate) is more suitable for low-noise RF/analog applications than those operated in conventional mode (V_body=V_source). Detailed low-frequency noise properties of these two modes of device operation were compared for 0.31-μm gate MOSFET's, in which NMOS's are surface-channel devices (S.C.) and PMOS's are buried-channel (B.C.) devices. Experimental data show that when the devices are biased at same transconductance, the low-frequency noise in DT mode is 30 times lower (at g_m=2.2×10^-3 S) than that in the conventional mode for the B.C. devices and ten times (at g_m=2.0×10 ^-3 S) lower for the S.C. devices     

V-band high-efficiency high-power AlInAs/GaInAs/InP HEMT's

The authors report on the state-of-the-art power performance of InP-based HEMTs (high electron mobility transistors) at 59 GHz. Using a 448-μm-wide HEMT with a gate length of 0.15 μm, an output power of 155 mW with a 4.9-dB gain and a power-added efficiency of 30.1% were obtained. By power-combining two of these HEMTs, an output power of 288 mW with 3.6-dB gain and a power-added efficiency of 20.4% were achieved. This is the highest output power reported with such a high efficiency for InP-based HEMTs, and is comparable to the best results reported for AlGaAs/InGaAs on GaAs pseudomorphic HEMTs at this frequency     

Low-frequency noise behavior of 0.15-μm gate-lengthlattice-matched and lattice-mismatched MODFETs on InP substrates

Experimental data are presented on equivalent gate noise voltage from 1 to 10⁵ Hz obtained from lattice-matched and strained InGaAs quantum-well modulation-doped field effect transistors (MODFETs). In both types of devices excess generation-recombination (g-r) noise is observed at or below 100 Hz above an `apparent' background 1/f noise with spectral intensity ranging from 0.5×10^-17 to 2×10^-17 V²-Hz^-1-cm² at 1 Hz. These results are comparable to those reported by S.M.J. Liu et al. (1986) for the pseudomorphic MODFETs     

Physical mechanisms limiting the manufacturing uniformity ofmillimeter-wave power InP HEMT's

We have developed a methodology to diagnose the physical mechanisms limiting the manufacturing uniformity of millimeter-wave power InAlAs/InGaAs HEMT's on InP. A statistical analysis was carried out on dc figures of merit obtained from a large number of actual devices on an experimental wafer. correlation studies and principal component analysis of the results indicated that variations in Si delta-doping concentration introduced during molecular-beam epitaxy accounted for more than half of the manufacturing variance. Variations in the gate-source distance that is determined by the electron-beam alignment in the gate formation process were found to be the second leading source of manufacturing variance. The statistical methodology used in this work is suitable for continuous process yield diagnostics and improvement in a manufacturing environment     

Low-frequency noise in n-GaN

Low-frequency noise has been investigated in the hexagonal polytype of n-type gallium nitride (GaN) with equilibrium electron concentration at 300 K n ₀⋍7×10¹⁷ cm⁻³. The frequency and temperature dependence of the noise spectral density S _I/I² was studied in the range of analysis frequencies f from 20 Hz to 20 kHz in the temperature range from 80 to 400 K. Over the entire temperature range the frequency dependence of the dark noise is close to S _I/I²∼1/f (flicker noise). The rather weak temperature dependence of the noise level is characterized by very high values of the Hooge constant α⋍5–7. These large α values indicate a rather low level of structural quality of the material. The effects of infrared and band-to-band illumination on low-frequency noise in GaN are studied here for the first time. The noise level is unaffected by illumination with photon energy E _ph<E _g (E _g is the band gap) even for a relatively high value of the photoconductivity Δσ⋍50%. Band-to-band illumination (E _ph⩾E _g) influences the low-frequency noise level over the entire investigated temperature range. At relatively high temperatures the influence of illumination is qualitatively similar to that of band-to-band illumination on low-frequency noise in Si and GaAs. At relatively low temperatures the influence of illumination on the noise in GaN is qualitatively different from the results obtained earlier for Si and GaAs. Fiz. Tekh. Poluprovodn. 32, 285–289 (March 1998)     

InP mixer diodes with etched via ohmic contacts

InP mixer diodes processed with Ag/TiW/Au Schottky diodes have exhibited a noise figure of 6.5?7.0 dB at 94 GHz. InP surface preparation is shown to be critical in diode performance. An indium-stabilised surface has resulted in a barrier height of 0.45 eV.     

Low-conductance drain (LCD) design of InAlAs/InGaAs/InP HEMT's

The concepts of the low-conductance drain (LCD) design approach for lattice-matched InAlAs/InGaAs/InP HEMTs are demonstrated for improved device performance. The tradeoff for LCD HEMT characteristics is a tapered current gain cutoff frequency f_t under high drain-to-source bias. This behavior is, in principle, due to the fact that the LCD approach increases the effective gate length of the HEMTs in exchange for reduced peak channel electric field. Two-dimensional PISCES simulation was used to optimize the improvements while simultaneously minimizing this undesirable effect for an LCD HEMT structure     

High-performance submicrometer gatelength GaInAs/InP compositechannel HEMT's with regrown ohmic contacts

This letter reports DC and RF performance of 0.25 μm gatelength GaInAs/InP composite channel HEMT's with nonalloyed, regrown ohmic contacts by MOCVD. Regrown channel contacts are used to achieve low contact resistance (0.35 Ω-mm) to (50 Å) GaInAs/(150 Å) InP composite channel HEMT's. High transconductance (600 mS/mm), high full channel current (650 mA/mm), and high peak cut-off frequencies (F_t=70 GHz, F_max=170 GHz) are observed. Contact transfer resistance of regrown channel contacts is compared to conventional alloyed contacts for varying GaInAs/InP channel composition     

High-energy and recombination-induced electroluminescence ofInAlAs/InGaAs HEMT's lattice-matched to InP substrates

We report room-temperature measurements of the high-energy electroluminescence (EL) of InAlAs/InGaAs HEMT's lattice-matched to InP substrates. We found that both the carrier temperature and the intensity obtained from the EL signal for the 1.4-1.7 eV energy range drastically increases with increasing the variation in the potential at the drain edge in the channel. The observed features are consistent with the results of the spatial distribution measurement, which indicates that the EL comes from the drain edge. We further compared the bias-voltage dependence of the high-energy EL and the recombination-induced EL measured for the same device, and discussed the origin and the threshold energy of the respective luminescent processes     

Low-frequency noise properties of GaN Schottky barriers deposited on intermediate temperature buffer layers

Metal–semiconductor–metal (MSM) structures were fabricated by RF-plasma-assisted MBE using different buffer layer structures. One type of buffer structure consists of an A1N high-temperature buffer layer (HTBL) and a GaN intermediate temperature buffer layer (ITBL), another buffer structure consists of just a single A1N HTBL. Systematic measurements in the flicker noise and deep level transient Fourier spectroscopy (DLTFS) measurements were used to characterize the defect properties in the films. Both the noise and DLTFS measurements indicate improved properties for devices fabricated with the use of ITBL and is attributed to the relaxation of residue strain in the epitaxial layer during growth process.     

气体激光器的低频差拍噪声

用光学混频技术研究了平凹腔结构气体激光器的模差拍。实验中应用了不同腔长的He-Ne(6328)和Ar~ 激光器。根据腔长的随机变化、介质色散特性和模竞争效应解释了低频拍和连续噪声谱。     

Low-frequency noise in hot-carrier degraded nMOSFETs

This paper discusses the low-frequency (LF) noise in submicron nMOSFETs under controlled transistor aging by hot-carrier stress. Both traditional, steady-state LF noise as well as the LF noise under periodic large-signal excitation were found to increase upon device degradation, for both hydrogen passivated and deuterium passivated Si–SiO₂ interfaces. As hot-carrier degradation is slower in deuterium-annealed MOSFETs, so is the increase of the noise in these devices. The noise-suppressing effect of periodic OFF switching is gradually lost during hot-carrier degradation, as the LF noise under periodic large-signal excitation increases more rapidly than the LF noise in steady-state.