Hir-Ming Shieh

High performance symmetric double /spl delta/-doped GaAs/InGaAs/GaAs pseudomorphic HFETs grown by MOCVD

High performance double /spl delta/-doped GaAs/In/sub 0.25/Ga/sub 0.75/ As/GaAs pseudomorphic HFETs grown by low pressure MOCVD are reported. An extrinsic transconductance as high as 390 mS/mm, and a saturation current density as high as 980 mA/mm along with broad transconductance plateau at 300 K with a 1.5 /spl mu/m gate length, are achieved. >

A novel /spl delta/-doped GaAs/lnGaAs real-space transfer transistor with high peak-to-valley ratio and high current driving capability

A three-terminal /spl delta/-doped GaAs/In/sub 0.25/Ga/sub 0.75/As/GaAs real-space transfer transistor (RSTT) has been implemented by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) for the first time. We carried out an ohmic recess resulting in shallow alloyed contacts, electrically isolated from ohmic electrodes. An undoped low-growth-rate buffer layer was inserted between the collector and barrier to suppress the dopant out-diffusion from the substrate to the barrier. The proposed device with a 5/spl times/100 /spl mu/m/sup 2/ emitter channel revealed an extremely sharp charge injection, a broad valley range (>5 V), a high peak-to-valley current ratio up to 430000, and a high current driving capability at room temperature. These characteristics are, to our knowledge, among the highest reported values to date. >

On the improvement of gate voltage swings in delta -doped GaAs/In/sub x/Ga/sub 1-x/As/GaAs pseudomorphic heterostructures

Significant improvements in gate voltage swings in heterostructures prepared by low-pressure metalorganic chemical vapor deposition are discussed. Structures utilizing a compositionally graded In/sub x/Ga/sub 1-x/As channel exhibited a very flat transconductance region of 2 V. The gate voltage swings of single and double delta -doped GaAs/In/sub 0.25/Ga/sub 0.75/As/GaAs structures were 2.5 and 2.8 V, respectively. All structures also exhibited high extrinsic transconductance as well as high saturation current densities. >

Very high two‐dimensional electron gas concentrations with enhanced mobilities in selectively double‐δ‐doped GaAs/InGaAs pseudomorphic single quantum well heterostructures

In this letter a new type of GaAs/In0.25Ga0.75As/GaAs pseudomorphic single quantum well heterostructure by selectively double‐δ‐doping GaAs layers on both sides of the InGaAs channel grown by low‐pressure metalorganic chemical vapor deposition is demonstrated. An extremely high two‐dimensional electron gas concentration more than 1×1013 cm−2 with enhanced mobility of 2900 cm2/V s is achieved. This type of structure can easily break through the doping limitation in conventional heterostructures while keeping a high mobility.

Investigation of the electron transfer characteristics in multi-/spl delta/-doped GaAs FET's

GaAs field-effect transistors (FETs) utilizing multiple /spl delta/-doping profiles to generate different shape of equivalent channels were demonstrated. The proposed structures containing three different triple-/spl delta/-doping profiles were grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The theoretical and experimental results in the triple-/spl delta/-doped GaAs structures exhibit much superior device performance than that of conventional uniform-doped GaAs structure. Besides, the proposed structures with graded-like /spl delta/-doping profiles show significantly improved linearity of transfer characteristics when compared to that without graded-like triple-/spl delta/-doping structure. The structure also revealed an extrinsic transconductance as high as 180 mS/mm for a gate length of 2 /spl mu/m.

Characterization of high performance inverted delta-modulation-doped (IDMD) GaAs/InGaAs pseudomorphic heterostructure FET's

An inverted delta-modulation-doped (IDMD) GaAs/InGaAs pseudomorphic heterostructure grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) is demonstrated and discussed. The respective influences of delta-doping period and spacer thickness on the sheet carrier densities and mobilities are investigated. For a 1.5/spl times/80 /spl mu/m/sup 2/ gate, a reverse leakage current smaller than 10 /spl mu/A/mm (at -6.5 V), a drain-source breakdown voltage as high as 14.5 V, a maximum drain saturation current as high as 790 mA/mm, a maximum extrinsic transconductance as high as 250 mS/mm, a very broad gate voltage range of 3 V, and an electron saturation velocity up to 2.4/spl times/10/sup 7/ cm/s, are obtained at room temperature. A simple theoretical simulation on the IDMD structure is also compared with the experimental results. >

Influences of δ ‐doping time and spacer thickness on the mobility and two‐dimensional electron gas concentration in δ ‐doped GaAs/InGaAs/GaAs pseudomorphic heterostructures

A series of GaAs/In0.25Ga0.75As/GaAs pseudomorphic high electron mobility transistors (HEMTs) was grown by low‐pressure metalorganic chemical vapor deposition. The respective influences of δ‐doping time and spacer thickness on the two‐dimensional electron gas concentrations and the mobilities were studied. The maximum mobilities, μ=5600 and 22 000 cm2/V s at 300 and 77 K, respectively, appeared at a spacer thickness of 100 A with a δ‐doping time of 0.2 min. A δ‐doped GaAs/In0.25Ga0.75As/GaAs pseudomorphic HEMT with the above parameters was fabricated. This device revealed high saturation current density of 350 mA/mm, transconductance of 95 mS/mm, and broad maximum transconductance region of 2.5 V with geometry of 2×100 μm2 at room temperature. In addition, very high breakdown voltage (26 V) and low leakage current (≤2 μA at −26 V) were achieved.

An improved inverted /spl delta/-doped GaAs/InGaAs pseudomorphic heterostructure grown by MOCVD

This letter demonstrates a novel GaAs/In/sub 0.25/Ga/sub 0.75/As/GaAs pseudomorphic heterostructure with /spl delta/-doping on the buffer prepared by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The proposed device with a 1.5/spl times/80 /spl mu/m/sup 2/ gate reveals an extrinsic transconductance as high as 250 (305) mS/mm and a saturation current density as high as 790 (890) mA/mm at 300 (77) K. Significantly improvements on forward gate voltage swing (up to 3 V) and on reverse leakage current (smaller than 10 /spl mu/A/mm at -6.5 V) are demonstrated due to inverted parallel conduction (IPC) effect. We also carried out secondary-ion mass spectrometry (SIMS) profiles to confirm the quality of the proposed device. >

Mobility enhancement in double δ‐doped GaAs/InxGa1−xAs/GaAs pseudomorphic structures by grading the heterointerfaces

A novel double δ‐doped heterostructure employing symmetric graded InGaAs quantum wells as the active channel grown by low‐pressure metalorganic chemical vapor deposition (LP‐MOCVD) has been successfully fabricated. The proposed symmetrically graded InGaAs pseudomorphic structure manifests significantly improved electron mobility as high as 5300 (26 000) cm2/V s at 300 (77) K due to superior confinement and to the lower interface roughness scattering at GaAs/InGaAs heterointerfaces. We also carried out photoluminescence (PL) spectra and secondary‐ion mass spectrometry (SIMS) profiles to confirm the quality of the proposed structures.

A high-performance delta -doped GaAs/In/sub x/Ga/sub 1-x/As pseudomorphic high electron mobility transistor utilizing a graded In/sub x/Ga/sub 1-x/As channel

A delta -doped GaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (HEMT) utilizing a graded In composition InGaAs channel grown by low-pressure metalorganic chemical vapor deposition was demonstrated. This structure had an extrinsic transconductance as high as 175 (245) mS/mm and a saturation current density a high as 500 (690) mA/mm at 300 (77) K for a gate length of 2 mu m. The maximum transconductance versus gate bias extended over a broad and flat region of more than 2 V at 300 K. A low gate leakage current ( >