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     

Stress-related hydrogen degradation of 0.1-/spl mu/m InP HEMTs and GaAs PHEMTs

Hydrogen degradation of III-V field-effect transistors (FETs) is a serious reliability concern. Previous work has shown that threshold-voltage shifts induced by H/sub 2/ exposure in 1-/spl mu/m-channel InP high-electron mobility transitors (HEMTs) can be attributed to compressive stress in the gate due to the formation of TiH/sub x/ in Ti/Pt/Au gates. The compressive stress affects the device characteristics through the piezoelectric effect. This paper examined the H/sub 2/ sensitivity of 0.1-/spl mu/m strained-channel InP HEMTs and GaAs pseudomorphic HEMTs. After exposure to H/sub 2/, the threshold voltage V/sub T/ of both types of devices shifted positive. This positive shift in V/sub T/ is predicted by a model for hydrogen-induced piezoelectric effect. In situ V/sub T/ measurements reveal distinct time dependences of the V/sub T/ shifts, which are also consistent with stress-related phenomena.     

Super low-noise HEMTs with a T-shaped WSix gate

A T-shaped quarter-micron gate structure composed of WSi_x /Ti/Pt/Au has been developed for low-noise AlGaAs/GaAs HEMTs. The gate resistance R_g was reduced to 0.3 Ω for devices with 200 μm-wide gates despite using WSi_x, and the source resistance R_s reached 0.28 Ω mm by minimising the source-gate distance using a self-alignment technique. This HEMT exhibited the lowest reported noise figure of 0.54 dB with an associated gain of 12.1 dB at 12 GHz     

台面型InP/InGaAs PIN光伏探测器的p-InP低阻欧姆接触

研究了电子束蒸发淀积的非合金膜系Au/Pt/Ti/p-InP(2×1018cm-3)接触的物理特性,通过450℃、4 min的快速退火,获得了欧姆接触,其比接触电阻为7.3×10-5 Wcm2.接触电极退火后,采用离子溅射法淀积加厚电极Cr/Au.利用俄歇电子能谱(AES)进行深度剖面分析,表明Pt层能够相对有效地阻挡...     

Metallurgical stability of ohmic contacts on thin baseInP/InGaAs/InP HBT's

The metallurgical stability of ohmic contacts: Pt, Pt/Ti, Au/Ti, Au/Pt/Ti, and Au/Pt/Ti/W, on a 500 Å thick p⁺-InGaAs base of InP/InGaAs/InP HBTs have been investigated as a function of anneal temperature. All contacts were stable after a 300°C-30 s anneal. Pt contact failed at 350°C whereas Pt/Ti, Au/Ti, and Au/Pt/Ti contacts failed at 400°C. The failure mechanism was a collector leakage short owing to the penetration of Pt or Ti through the thin base. Only HBTs with Au/Pt/Ti/W contact were still functional after a 400°C anneal with no apparent shift in the turn-on voltage for the emitter and collector junctions     

High efficiency single pulse doped Al0.60In0.40As/GaInAs/InP HEMTs for Q-band power applications

Single pulse doped, 0.2 μm-gate Al_0.60In_0.40 As/GaInAs/InP HEMTs have been fabricated and characterised. The complete process sequence for the HEMTs includes SiN_x passivation and dry etched via hole fabrication. Power measurements at 44 GHz on a 10×60 μm² device yielded 225 mW output power, 5 dB associated gain, and 39% power added efficiency. The results indicate that the single pulse doped InP-based HEMTs are suitable for high power applications at Q-band     

Monolithic microwave amplifiers formed by ion implantation into LEC gallium arsenide substrates

A fabrication procedure for broad-band monolithic power GaAs integrated circuits has been demonstrated which includes formation of via holes through the 100-µm-thick GaAs substrate. A selective implant of²⁹Si ions into the GaAs substrate is used to dope the FET channel region to 1.2 × 10¹⁷cm^-3. The ohmic contacts are AuGe/Ni/Pt and the gates are Ti/Pt/Au. A 1.5-µm-thick circuit pattern is achieved using metal rejection assited by chlorobenzene treatment of AZ1350J photoresist. Using undoped Czochralski wafers of GaAs pulled from a pyrolytic boron nitride crucible, integrated amplifiers have been produced which deliver 28 ± 0.7 dBm from 5.7 to 11 GHz. These chips are 2 mm × 4.75 mm × 0.1 mm thick.     

Improved Long-Term Thermal Stability At 350°C Of TiB2–Based Ohmic Contacts On AlGaN/GaN High Electron Mobility Transistors

AlGaN/GaN High Electron Mobility Transistors (HEMTs) were fabricated with Ti/Al/TiB₂/Ti/Au source/drain Ohmic contacts and a variety of gate metal schemes (Pt/Au, Ni/Au, Pt/TiB₂/Au or Ni/TiB₂/Au) and subjected to long-term annealing at 350°C. By comparison with companion devices with conventional Ti/Al/Pt/Au Ohmic contacts and Pt/Au gate contacts, the HEMTs with boride-based Ohmic metal and either Pt/Au, Ni/Au or Ni/TiB₂/Au gate metal showed superior stability of both source-drain current and transconductance after 25 days aging at 350°C.     

GaAs surface plasma treatments for Schottky contacts

The properties of different rectifying metallizations (Al, Ti/Pt, WN_x) on GaAs have been investigated for various surface preparation procedures. In particular, in situ hydrogen plasma treatments were used to remove residual surface contamination (mainly O and C) and a nitrogen plasma to grow a thin mixed nitride layer. Al and Ti/Pt Schottky diodes with an ideality factor very close to 1, but with reduced barrier height, were found after the H₂ plasma as a consequence of H diffusion into GaAs. The Schottky barrier height was further reduced if a H₂ + N₂ plasma was performed. The N content in the sputtering environment during the WN_x deposition affects the diode properties of plasma-treated WN_x contacts. By increasing the N₂ partial pressure, the diode barrier height is reduced, probably due to nitridization of the GaAs surface. Such differences disappear after annealing the diodes in arsine overpressure at 800°C. WN_x contacts deposited under different conditions on H₂ plasma treated substrates also show a similar Schottky barrier height after such annealing.     

Use of Sn-doped GaAs for non-alloyed ohmic contacts to HEMTs

Segregation of Sn to the surface of MBE grown n⁺-GaAs layers allows fabrication of non-alloyed Ti/Pt/Au, Al or Ti/W ohmic contacts with low specific contact resistivities (1.1×10^-6 Ω·cm^-2). These contacts were used to realise high performance HEMTs (g_m=230 mS/mm for 1.0 μm gate length) in which Si is used as the dopant in the donor AlGaAs layer and Sn is employed in the GaAs contact layer     

Performance dependence of InGaP/InGaAs/GaAs pHEMTs on gatemetallization

The performance of InGaP-based pHEMTs as a function of gate metallization is examined for Mo/Au, Ti/Au, and Pt/Au gates. DC and microwave performance of pHEMT's with 0.7-μm gate lengths is evaluated. Transconductance, threshold voltage, f_t, and f_max are found to depend strongly on gate metallization. High-speed performance is achieved, with f_t of 41.3 GHz and f _max of 101 GHz using Mo/Au gates. The difference in performance between devices with different gate metallizations is postulated to be due to a combination of the difference in Schottky barrier heights and different gate-to-channel spacings due to penetration of the gate metal into the InGaP barrier layer     

Schottky barrier heights of n-type and p-type Al0.48In0.52As

The authors report electrical measurements on four different metal contacts which formed Schottky barriers to lightly doped complementary n- and p-type Al_0.48In_0.52As epitaxial material grown by molecular beam epitaxy on semi-insulating InP substrates. The Schottky contact metals studied were Au, Al, Pt, and tri-layer Ti/Pt/Au. The Schottky barrier heights varied from 0.560 eV for Al on n-type AlInAs to 0.905 eV for Al on p-type AlInAs, with intermediate values for the other metals studied. The sum of n- and p-type Schottky barrier heights for each metal contact ranged from 1.440 to 1.465 eV, in good agreement with the accepted Al_0.48In_0.52As bandgap value of 1.45 eV     

GaN p–n junction diode formed by Si ion implantation into p-GaN

²⁸Si⁺ implantation into Mg-doped GaN, followed by thermal annealing in N₂ was performed to achieve n⁺-GaN layers. The carrier concentrations of the films changed from 3×10¹⁷ (p-type) to 5×10¹⁹ cm⁻³ (n-type) when the Si-implanted p-type GaN was properly annealed. Specific contact resistance (ρ_c) of Ti/Al/Pt/Au Ohmic contact to n-GaN, formed by ²⁸Si⁺ implantation into p-type GaN, was also evaluated by transmission line model. It was found that we could achieve a ρ_c value as low as 1.5×10⁻⁶ Ω cm² when the metal contact was alloyed in N₂ ambience at 600 °C. Si-implanted GaN p–n junction light-emitting diodes were also fabricated. Electroluminescence measurements showed that two emission peaks at around 385 and 420 nm were observed, which could be attributed to the near band-edge transition and donor-to-acceptor transition, respectively.     

Studies of CW lasing action in CO2-CO,N2O-CO, CO2-H2O, and N2O-H2O mixtures pumped by blackbody radiation

A proof of principle experiment to evaluate the efficacy of CO and H₂O in increasing the power output for N₂O and CO ₂ lasing mixtures has been conducted and theoretically analyzed for a blackbody radiation-pumped laser. The results for N₂ O-CO, CO₂-CO, N₂O-H₂O and CO₂-H₂O mixtures are presented. Additions of CO to the N₂O lasant increased power up to 28% for N₂O laser mixtures, whereas additions of CO to the CO₂ lasant, and the addition of H₂O to both the CO₂ and N₂O lasants, resulted in decreased output power     

Application of indium-tin-oxide with improved transmittance at 1.3μm for MSM photodetectors

The optical transmittance of indium-tin oxide (ITO) at a wavelength of 1.3 μm has been improved by adding forming gas (H₂ /N₂) to the Ar sputtering gas. It is shown that the presence of H₂ in the plasma decreases the carrier concentration in ITO and increases the optical transmittance of a 320 nm-thick ITO film from 69.7% to 99.5%. The application of the high transmittance ITO to the fabrication of metal-semiconductor-metal (MSM) photodiodes on InAlAs/InGaAs heterostructures has resulted in an improvement of responsivity from 0.6 A/W to 0.76 A/W. This is double the responsivity of 0.39 A/W obtained for Ti/Au detectors. A 3-dB bandwidth of 6 GHz was obtained for the high transparency ITO device with 3 μm fingers and gaps and with an area of 50 μm×50 μm     

Low-pressure H2/N2 annealing on indium tin oxide film

Annealing of indium tin oxide (ITO) film in low-pressure H₂/N₂ was investigated. On carefully selecting the annealing process window, apparent electrical property improvement as well as good optical property can be obtained. It was found that ITO annealed with 2 Pa, H₂/N₂:6/6 sccm, at 500 °C for an hour can increase its electrical conductivity 60% more than ITO without annealing, 58% more than ITO annealed with pure H₂. An annealed ITO without specially selected recipe can easily possess worse electrical and optical properties than that without annealing. It can be explained that annealing ITO in a hydrogen-contained environment can lead to hydrogen reduction–oxygen vacancy playing a donor role in ITO; however, annealing also provides the energy to remove ITO material defects including donors.     

Ultra-short 25-nm-gate lattice-matched InAlAs/InGaAs HEMTs withinthe range of 400 GHz cutoff frequency

We have succeeded in fabricating ultra-short 25-nm-gate InAlAs/InGaAs high electron mobility transistors (HEMTs) lattice-matched to InP substrates. The two-step-recessed gate technology and low temperature processing at below 300°C allowed the fabrication of such ultra-short gates. DC measurements showed that the 25-nm-gate HEMT had good pinchoff behavior. We obtained a cutoff frequency f_T of 396 GHz, within the range of 400 GHz f_T, for the 25-nm-gate HEMT. This f_T is the highest value get reported for any type of transistor, and the gate length of 25 nm is the shortest value ever reported for any compound semiconductor transistor that exhibits device operation     

On the correlation between drain-gate breakdown voltage andhot-electron reliability in InP HEMTs

By comparing devices with different recess widths, we show that the off-state drain-gate breakdown voltage (BV_DG) may give totally misleading indications on the reliability of lattice-matched InP HEMTs under hot-electron (HE) and impact ionization conditions, from both standpoints of gradual and catastrophic degradation. Since the hot-electron degradation effects observed in our HEMTs are quite common, we believe that our results should be considered as a general caveat whenever indications on HE HEMT robustness are inferred from BV_DG measurements     

Effects of post-deposition anneal on the electrical properties ofSi3N4 gate dielectric

The effects of postdeposition anneal of chemical vapor deposited silicon nitride are studied. The Si₃N₄ films were in situ annealed in either H₂(2%)/O₂ at 950°C or N₂O at 950°C in a rapid thermal oxidation system. It is found that an interfacial oxide was grown at the Si₃N₄/Si interface by both postdeposition anneal conditions. This was confirmed by thickness measurement and X-ray photoelectronic spectroscopy (XPS) analysis. The devices with H₂ (2%)/O₂ anneal exhibit a lower gate leakage current and improved reliability compared to that of N₂O anneal. This improvement is attributed to a greater efficiency of generating atomic oxygen in the presence of a small amount of hydrogen, leading to the elimination of structural defects in the as-deposited Si₃N ₄ film by the atomic oxygen. Good drivability is also demonstrated on a 0.12 μm n-MOSFET device     

Sem,auger spectroscopy and ion backscattering techniques applied to analyses of Au/refractory metallizations

The concurrent application of the SEM, AES, X-ray diffractometry and Rutherford Backscattering (RBS) techniques to Au/refractory metallizations is analyzed with respect to the study of thin film interdiffusion, intermetallic formation, microcracking and oxidation phenomena. The SEM in the backscatter electron image mode was used for resolution of intermetallic compounds and interdiffusion products, while AES and RBS analyses were used to obtain depth-composition profiles. The metallizations studied were Ta/Pt/Ta/Au and W/Au. The combination of Ta/Pt/Ta and Ti/Pt have been shown to be effective barriers to gold-silicon interdiffusion. Defects in the tungsten barrier were found to result in silicon migration to the front surface and gold migration toward the substrate at temperatures between 550°C-700°C . The diffusion constants for Au-Ta and Au-Pt interdiffusion have been determined from the AES data.