Rong-Tay Hsu

Characteristics of In0.52Al0.48As/InxGa1−xAs HEMT’s with various InxGa1−xAs channels

Abstract High-linearity In0.52Al0.48As/InxGa1−xAs HEMT’s have been successfully fabricated by low-pressure metal organic chemical vapor deposition (LP-MOCVD). The studied devices exhibit high transconductance, low leakage current, high breakdown, and high-linearly operational regime due to good carrier confinement well as the low temperature growth In0.52Al0.48As barrier layer significantly suppresses buffer leakage current. Experimentally, linear operation current regime and gate voltage swing are improved in the structure utilizing a compositionally graded InxGa1−xAs channel due to the compositionally graded InxGa1−xAs channel enhance the device carrier mobility and confinement. An extrinsic transconductance as high as 302 mS/mm at gate length of 1.5 μm is achieved for the In0.6Ga0.4As channel structure.

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. >

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.

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 ( >

Comparison of Al0.32Ga0.68N ∕ GaN Heterostructure Field-Effect Transistors with Different Channel Thicknesses

Al 0. 32 Ga 0. 68 N/GaN heterostructure field-effect transistors (HFETs) grown by low-pressure metallorganic chemical vapor deposition are successfully fabricated. A Mg-doped insulating GaN layer is inserted to suppress the leakage current, improve the breakdown voltages, and yield excellent pinch-off characteristics. Moreover, HFETs with different channel thicknesses of 1200, 1500, and 1800 A are investigated. Experimental results show that an HFET with a 1800 A thick channel layer has the highest electron mobility, electron concentration, drain current, and extrinsic transconductance.

Characteristics of a δ ‐doped GaAs/InGaAs p‐channel heterostructure field‐effect transistor

A δ‐doped GaAs/In0.2Ga0.8As p‐channel heterostructure field‐effect transistor grown by low‐pressure metalorganic chemical vapor deposition is demonstrated. The mobilities and two‐dimensional hole gas concentrations at 300 (77) K are 260 (2600) cm2/v s and 1012 (5.5×1011) cm−2, respectively. For a gate length of 1.5 μm, the maximum extrinsic transconductances are 15 mS/mm at 300 K and 24 mS/mm at 77 K. The high transconductances extend a wide range versus gate voltage.

Comparative study of In0.52Al0.48As/InxGa1−xAs/InP high-electron-mobility transistors with a symmetrically graded and an inversely graded channel

InP-based InAlAs/InxGa1?xAs/InP high-electron-mobility transistors (HEMTs) with a symmetrically graded channel (SGC-HEMT) and an inversely graded channel (IGC-HEMT) were fabricated and studied. The SGC-HEMT exhibits better Hall, dc and RF characteristics than the IGC-HEMT because there are more electrons accumulated in the symmetrically graded channel. However, the IGC-HEMT has better thermal stability than the SGC-HEMT because the former has higher bandgap discontinuity at the channel/buffer heterojunction and less Coulomb scattering from a ?-doped layer. Furthermore, the IGC-HEMT sustains larger output power than the SGC-HEMT attributed to better breakdown characteristics. Therefore, HEMTs with the symmetrically graded and an inversely graded channel are suitable for high-speed and high-power applications, respectively.

Investigation of InGaP/GaAs heterojunction bipolar transistor with doping graded base

An n-p-n InGaP/GaAs heterojunction bipolar transistor (HBT) using a graded base doping profile has been fabricated by low pressure metalorganic chemical vapor deposition. A current gain of 77 and a base sheet resistance of 251 Ω/sq are achieved in the graded-base HBT. Compared to the graded-base structure, the nongraded-base structure has a lower current gain (68) and a higher base sheet resistance (294 Ω/sq). Furthermore, the studied graded-base HBT device also shows better microwave characteristics. The measured unity current-gain cutoff frequency (fT) can be improved from 18 to 22 GHz. The functional dependences of current gain, base sheet resistance, and microwave characteristics on the base doping profile are attributed to the graded-doping enhanced built-in field across the base and higher base doping at the emitter edge.

Low Dark Current InGaAs(P)/InP p–i–n Photodiodes

Planar InGaAs(P)/InP p–i–n photodiodes have been successfully fabricated by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). High-quality and uniform epitaxial layers are obtained. It is noted that the InGaAs layer background concentration is as low as 4.5 ×1013 cm-3. The dark current is significantly reduced by using a wider-band-gap material of quaternary InxGa1-xAsyP1-y as a cap layer to reduce the device surface leakage current. In addition, the device becomes highly photosensitive due to the reduction of the absorption of the radiation in the narrow-band-gap InxGa1-xAsyP1-y cap layer. The p–i–n photodiode with a wide-band-gap InP cap layer exhibits a dark current as low as 60 pA at -10 V bias, corresponding to a dark current density of 4.2×10-7 A/cm2.

Characteristics of graded‐like multiple‐delta‐doped GaAs field effect transistors

Multiple‐δ‐doped GaAs field effect transistors using graded‐like δ‐doping profile are demonstrated and investigated. An extremely high carrier density of 1.2×1013 (7.9×1012) cm−2 along with an enhanced Hall mobility of 1700 (3300) cm2/v s at 300 (77) K for a triple‐δ‐doped GaAs structure are achieved. The dc characteristic reveals an extrinsic transconductance as high as 110 mS/mm at room temperature with a gate length of 2 μm. Three separated peaks in the transconductance versus gate bias curve are observed. Meanwhile, a broad and flat transconductance region is obtained.