J.M. Ballingall

Ultra-low-noise cryogenic high-electron-mobility transistors

Quarter-micrometer gate-length high-electron-mobility transistors (HEMTs) for cryogenic low-noise application with very low light sensitivity have been developed. At room temperature, these exhibit a noise figure of 0.4 dB with associated gain of 15 dB at 8 GHz. At a temperature of 12.5 K the minimum noise temperature of 5.3+or-1.5 K has been measured at 8.5 GHz, which is the best noise performance observed to date for any microwave transistors. The results clearly demonstrate the potential for low-temperature low-noise applications. >

Advances in HEMT Technology and Applications

High electron mobility transistors (HEMTs) have demonstrated unsurpassed transistor performance in the millimeter-wave range--at 60 GHz, results include a minimum noise figure of 2.3 dB with 4.0 dB associated gain, maximum small-signal gain of 11.7 dB, output power of 50 mW, power density of 0.43 W/mm and maximum power-added efficiency of 28%. The principles of HEMT operation and design are described, followed by a summary of the current state-of-the-art in noise and power performance, and discussion of several applications.

High quality (111)B GaAs, AlGaAs, AlGaAs/GaAs modulation doped heterostructures and a GaAs/InGaAs/GaAs quantum well

We report the successful growth of high quality molecular beam epitaxy (MBE) GaAs, AlGaAs, AlGaAs/GaAs modulation doped heterostructures and a GaAs/InGaAs/GaAs quantum well on GaAs (111)B substrates. Modulation doped heterostructures show a 77 K mobility of 145 500 cm2/V s with a sheet density of 5.0×1011 cm−2. Photoluminescence of (111)B GaAs indicates a lower carbon incorporation than achieved on (100) substrates. The low growth temperature and high material quality obtainable in (111)B growth will provide advantages for laser diodes and heterostructure field effect transistors.

A 0.15 mu m gate-length pseudomorphic HEMT

A 0.15- mu m-gate-length double-heterojunction pseudomorphic HEMT (high electron mobility transistor) that exhibits state-of-the-art power and noise performance is reported. Power results include record power-added efficiencies of 51%, 41% and 23% at 35, 60 and 94 GHz, respectively, and output powers of 139 mW at 60 GHz and 57 mW at 94 GHz. Measured minimum noise figures of 0.55 dB at 18 GHz and 1.8 dB at 60 GHz are reported. It is suggested that because of its demonstrated performance and continued rapid rate of improvement, the pseudomorphic HEMT should be the preferred transistor for a number of millimeter-wave applications, used either as a discrete device in high-performance hybrid amplifiers or integrated into GaAs-based MMICs (monolithic microwave integrated circuits).<<ETX>>

Novel pseudomorphic high electron mobility transistor structures with GaAs‐In0.3Ga0.7As thin strained superlattice active layers

The thin strained superlattice (TSSL) concept is introduced as a means for extending the practical range of application for pseudomorphic Inx Ga1−x As on GaAs. Growth and characterization results are presented for pseudomorphic high electron mobility transistor structures with GaAs‐In0.3 Ga0.7 As TSSL active layers grown by molecular beam epitaxy. The TSSLs are composed of three periods of GaAs(15 A)‐ In0.3 Ga0.7 As(h2 ), where h2 ranges from 30 to 52 A. Modulation doping of the TSSLs is provided by atomic planar‐doped Al0.3 Ga0.7 As overlayers with 45 A undoped spacers. 77 K Hall effect and transmission electron microscopy reveal that relatively thick TSSLs can be grown with high electronic and structural quality, comparable to much thinner In0.3 Ga0.7 As single quantum wells. Results are compared with a model for critical layer thickness and discussed in light of in situ reflection high‐energy electron diffraction measurements.

0.1-&#181;m Gate-length pseudomorphic HEMT's

AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors (HEMTs) with a gate length of 0.1 µm have been successfully fabricated. The HEMTs exhibit a maximum transconductance of 540 mS/mm with excellent pinch-off characteristics. A maximum stable gain (MSG) as high as 18.2 dB was measured at 18 GHz. At 60 GHz the device has demonstrated a minimum noise figure of 2.4 dB with an associated gain of ∼6 dB. These are the best gain and noise results reported to date for HEMTs.

Extremely high gain, low noise InAlAs/InGaAs HEMTs grown by molecular beam epitaxy

High-performance InAlAs/InGaAs planar-doped HEMTs (high-electron-mobility transistors) lattice-matched to InP have been fabricated with a 0.25- mu m T-gate. A maximum extrinsic transconductance g/sub m/ of 900 mS/mm, corresponding to an intrinsic g/sub m/ of 1640 mS/mm, was obtained at room temperature. RF measurements at 18 GHz yielded a minimum noise figure of 0.5 dB with an associated gain of 15.2 dB and a maximum stable gain of 20.9 dB. At 58 GHz, the devices exhibited a 1.2-dB minimum noise figure with an 8.5-dB associated gain. At 63 GHz, a maximum available gain of 15.4 dB was measured for a single-stage amplifier. This value, extrapolated to -6 dB/octave, yielded a maximum frequency of oscillation f/sub max/ of 380 GHz, which is the highest f/sub max/ ever reported for any transistor. A three-stage HEMT amplifier exhibited an average noise figure of 3.0 dB with a gain of 22.0+or-0.2 dB from 60-65 GHz.<<ETX>>

Subpicosecond carrier response of unannealed low-temperature-grown GaAs vs temperature

The subpicosecond carrier lifetime of an unannealed molecular beam epitaxial layer of GaAs grown at ∼210°C has been demonstrated between 10 and 290K through optoelectronic switching and all-optical pump-probe measurements. The low room-temperature resistivity of the as-grown layers, believed to arise from hopping conductivity through defect sites, has been observed to increase as the sample temperature was lowered, allowing ultrafast switching measurements to be performed using the low-temperature-as-grown GaAs as a photoconductive element. After illumination by 100 femtosecond optical pulses, photogenerated carriers in the sample have rapidly relaxed, returning the material to its high-resistivity state in less than 1 ps. This indicates that the precipitates present in post-annealed samples are not required for the fast relaxation of photoexcited carriers in low-temperature-grown GaAs. Ultrafast switching measurements on a post-annealed version of the GaAs film also resulted in the generation of similar, 0.6 ps full width at half maximum pulses.

Comparison of high quality (111)B and (100) AlGaAs grown by molecular beam epitaxy

State‐of‐the‐art quality Al0.3Ga0.7As was achieved on both (111)B and (100) GaAs by molecular beam epitaxy. Low‐temperature photoluminescence linewidths of 2.9 and 2.4 meV were obtained for (111)B and (100) Al0.3Ga0.7As, grown at 650 and 700 °C, respectively, with nearly equivalent integrated luminescence intensity. This is the narrowest linewidth ever reported for (111) AlGaAs. The low growth temperature and high material quality of (111)B Al0.3Ga0.7As is expected to be an important factor to the future development of both electronic and optical heterostructure devices.

Very high performance 0.15 mu m gate-length InAlAs/InGaAs/InP lattice-matched HEMTs

State-of-the-art high-electron-mobility-transistor (HEMT) devices have been fabricated on InAlAs/InGaAs/InP. Devices with 30- mu m and 50- mu m gate widths and 0.15- mu m gate length were fabricated using an all-electron-beam lithography process. After mesa formation, ohmic contacts were formed using a standard NiAuGe metallization. The contacts were annealed using a rapid thermal annealer. Typical ohmic contact resistance was approximately 0.13 Omega -mm. This is the same as the typical contact for the GaAs-based pseudomorphic HEMT result. Gates were defined using a trilayer resist scheme and recessed using a wet chemical etch to reach the desired channel current. A TiPtAu metallization forms the gate. The devices exhibited performance superior to most other low noise HEMT devices. It is found that the gate leakage current increases as recess depth increases. This current increase seems to degrade noise performance.<<ETX>>