Yeong-Jia Chen

Characteristics of In/sub 0.425/Al/sub 0.575/As-InxGa/sub 1-x/As metamorphic HEMTs with pseudomorphic and symmetrically graded channels

In/sub 0.425/Al/sub 0.575/As-In/sub x/Ga/sub 1-x/As metamorphic high electron mobility transistors (MHEMTs) with two different channel designs, grown by molecular beam epitaxy (MBE) system, have been successfully investigated. Comprehensive dc and high-frequency characteristics, including the extrinsic transconductance, current driving capability, device linearity, pinch-off property, gate-voltage swing, breakdown performance, unity-gain cutoff frequency, max. oscillation frequency, output power, and power gain, etc., have been characterized and compared. In addition, complete parametric information of the small-signal device model has also been extracted and discussed for the pseudomorphic channel MHEMT (PC-MHEMT) and the V-shaped symmetrically graded channel MHEMT (SGC-MHEMT), respectively.

High breakdown characteristic /spl delta/-doped InGaP/InGaAs/AlGaAs tunneling real-space transfer HEMT

A novel /spl delta/-doped InGaP/InGaAs/AlGaAs tunneling real-space transfer high-electron mobility transistor (TRST-HEMT) has been successfully fabricated by low-pressure metal organic chemical vapor deposition (LP-MOCVD). Three-terminal N-shaped negative differential resistance (NDR) phenomenon due to the hot electrons real-space transfer (RST) at high electric field is observed. Two-terminal gate-to-drain breakdown voltage is more than 40 V with a leakage current as low as 0.27 mA/mm. High three-terminal on-state breakdown voltage as high as 19.2 V and broad plateau of current valley as high as 15 V are achieved. These characteristics are attributed to the use of high Schottky barrier height, high bandgap of InGaP Schottky layer, /spl delta/-doping, and GaAs subspacer layers. The measured maximum peak-to-valley ratio (PVR) value is 2.7.

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.

High-temperature thermal stability performance in /spl delta/-doped In/sub 0.425/Al/sub 0.575/As--In/sub 0.65/Ga/sub 0.35/As metamorphic HEMT

We report, to our knowledge, the best high-temperature characteristics and thermal stability of a novel /spl delta/-doped In/sub 0.425/Al/sub 0.575/As--In/sub 0.65/Ga/sub 0.35/As--GaAs metamorphic high-electron mobility transistor. High-temperature device characteristics, including extrinsic transconductance (g/sub m/), drain saturation current density (I/sub DSS/), on/off-state breakdown voltages (BV/sub on//BV/sub GD/), turn-on voltage (V/sub on/), and the gate-voltage swing have been extensively investigated for the gate dimensions of 0.65/spl times/200 /spl mu/m/sup 2/. The cutoff frequency (f/sub T/) and maximum oscillation frequency (f/sub max/), at 300 K, are 55.4 and 77.5 GHz at V/sub DS/=2 V, respectively. Moreover, the distinguished positive thermal threshold coefficient (/spl part/V/sub th///spl part/T) is superiorly as low as to 0.45 mV/K.

Characteristics of Spike-Free Single and Double Heterostructure-Emitter Bipolar Transistors

In this study, we propose single and double heterostructure-emitter bipolar transistors (SHEBTs and DHEBT, respectively) with undoped spacers inserted on both sides of the base. The spike-free HEBT is achieved by solving Poissons equation. The SHEBT and DHEBT with 100 A spacers exhibit common-emitter current gains of 200 and 120, along with offset voltages of 80 and 50 mV, respectively. Meanwhile, the current gains of the passivated SHEBT and DHEBT reach 360 and 180, respectively. The passivated SHEBT with 100 A spacer exhibits a current gain over unity at ultralow current densities of 10-5 A/cm2. Additionally, experimental results for different spacer thicknesses demonstrate that the 100 A spacer yields the highest current gain.

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.

Improved Step-Graded-Channel Heterostructure Field-Effect Transistor

A heterostructure field-effect transistor with a step-graded channel has been successfully fabricated. The conduction electrons are distant from the AlGaAs/InGaAs interface; thus the Coulomb scattering is reduced, and consequently, electron mobility is increased. A high drain-current density and a large gate-voltage swing can be obtained. For a 1.2×100 µm2 gate, the maximum saturation drain-current density is 373 mA/mm and the maximum extrinsic transconductance is 148 mS/mm with a gate-voltage swing of 1.9 V.

Enhancement-mode In0.52Al0.48As/In0.6Ga0.4As tunneling real space transfer high electron mobility transistor

An enhancement-mode In0.52Al0.48As/In0.6Ga0.4As tunneling real-space transfer high electron mobility transistor (HEMT) was fabricated. The studied device operates as a conventional enhancement-mode HEMT under a low gate electrode bias. As the gate electrode bias increases, the electric field applied between the gate electrode and the InGaAs channel increases and the electrons in the channel become “hot.” If the transverse field is sufficiently large, then the electrons in the InGaAs channel layer may have enough energy to overcome the barrier and tunnel into the gate electrode, thus IDS decreases as IG increases. Therefore, pronounced N-shaped negative differential resistance phenomenon and negative transconductance are observed in the studied device.

Improved characteristics of metamorphic InAlAs/InGaAs high electron mobility transistor with symmetric graded InxGa1-xAs channel

A metamorphic high electron mobility transistor with symmetric graded InxGa1−xAs channel has been successfully grown by molecular beam epitaxy system. Due to the lower interface roughness scattering, the improved electron mobility as high as 9500(30600)cm2∕Vs at 300(77)K is achieved. By using the self-consistent method, three subbands in the graded channel are found, which is matched to the Shubnikov-de Haas data. By using the graded channel, In0.425Al0.575As Schottky layer, and undoped InP setback layer, a high gate breakdown voltage of 24V is obtained. Meanwhile, the measured current gain cutoff frequency fT and maximum oscillation frequency fmax for a 1.5μm gate device are 18.9 and 48.4GHz, respectively.