In this letter we report the effect of vertical scaling on the optical and electrical performance of mid-wavelength infrared heterojunction phototransistors based on type-II InAs/GaSb/AlSb superlattices. The performance of devices with different base thickness was compared as the base was scaled from 60 down to 40 nm. The overall optical performance shows enhancement in responsively, optical gain, and specific detectivity upon scaling the base width. The saturated responsivity for devices with 40 nm bases reaches 8845 and 9528 A W-1 at 77 and 150 K, respectively, which is almost five times greater than devices with 60 nm bases. The saturated optical gain for devices with 40 nm bases is measured as 2760 at 77 K and 3081 at 150 K. The devices with 40 nm bases also exhibit remarkable enhancement in saturated current gain, with 17690 at 77 K, and 19050 at 150 K.

http://iopscience.iop.org/article/10.1088/1361-6528/aa5849/pdf

Impact of scaling base thickness on the performance of heterojunction phototransistors

The interesting ammonia sensing current–voltage ( I–V ) characteristics of a Pt/AlGaN/GaN Schottky diode are firstly studied and demonstrated. It is found that the ammonia sensitivity is increased by increasing the temperature. Yet, the sensitivity is decreased when the temperature is higher than 423 K. Experimentally, the studied device exhibits a good sensitivity of 13.1 under exposing to a relatively low concentration ammonia gas of 35 ppm NH 3 /air. In addition, the good sensing performance of the studied device is demonstrated over a wide operating temperature regime from 298 K to 473 K. A highest ammonia sensing response of 182.7 is found at 423 K while a 10,000 ppm NH 3 /air gas is introduced.

Ammonia sensing characteristics of a Pt/AlGaN/GaN Schottky diode

High performance UV photodetector based on MoS2 layers grown by pulsed laser deposition technique

An AlGaN/GaN metal–oxide–semiconductor high-electron mobility transistor (MOS-HEMT) that uses a high-k TiO2 gate insulator is demonstrated. TiO2 films are annealed at 300 °C and 600 °C in N2 or O2 following the deposition of an oxide layer. Experimental results reveal that the 300 °C N2-annealed TiO2/GaN MOS capacitor has the smallest interface traps of any of the studied devices. The 300 °C N2-annealed oxide interlayers between the GaN and the gate metal reduce the gate leakage current and improve the dc, high-frequency, and noise characteristics. The gate leakage current of the 300 °C N2-annealed MOS-HEMT is more than 3 orders of magnitude less than that of the baseline HEMT. This brief is the first to fabricate a GaN-based MOS-HEMT using an N2-annealed TiO2 gate insulator.

Improved AlGaN/GaN Metal–Oxide– Semiconductor High-Electron Mobility Transistors With TiO 2 Gate Dielectric Annealed in Nitrogen

An interesting Pt/AlGaN/GaN Schottky-type ammonia gas sensor is fabricated and studied. Both the steady-and transient-state behaviors of ammonia adsorption reactions are investigated. At 150°C, significant ammonia detection is observed under a low ammonia concentration of 35-ppm NH3/air. Moreover, a high ammonia sensing response of 18300% and the large Schottky barrier variation ratio A.φb/φb, air of 13.8% are observed upon exposure to a 1% NH3/air gas at 150°C. The presence of dipoles at the metal-semiconductor interface leads to a lowering effect of Schottky barrier height and a larger current. In addition, based on thermodynamics, in contrast with a hydrogen adsorption reaction, the ammonia adsorption reaction is an endothermic reaction. Consequently, the studied NH3 sensor structure provides the promise to integrate high-performance AlGaN/ GaN-based optoelectronic and microwave devices on a single chip.

Ammonia Sensing Properties of a Pt/AlGaN/GaN Schottky Diode

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.

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

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.

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

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.

/pdf/low-dark-current-ingaas-p-inp-p-i-n-photodiodes-i5paw4h8in.pdf

Low dark current InGaAs(P)/InP p-i-n photodiodes

High-linearity In 0.52 Al 0.48 As/In 0.53 Ga 0.47 As doped channel transistor (DCFET) was successfully fabricated by low-pressure metal organic chemical vapor deposition (LP-MOCVD). Due to the presence of doped InGaAs channel, undoped InAlAs barrier layer and low-temperature growth InAlAs buffer layer, good carrier confinement, improved breakdown and a wide transconductance operation regime are expected. Experimentally, for a 1.5 × 100 μm 2 device, high-transconductance of 291 mS/mm, high-gate-drain breakdown voltage of 20.2 V, high-turn-on voltage of 0.78 V, wide operation regime of 288 mA/mm as well as significantly improved gate voltage swing of 1.05 V are achieved. Additionally, the studied device shows good temperature characteristics. The performance indicates the promise for high-power and high-temperature applications.

InAlAs/InGaAs doped channel heterostructure for high-linearity, high-temperature and high-breakdown operations

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.

Rong-Tay Hsu

Papers

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

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

Low dark current InGaAs(P)/InP p-i-n photodiodes

InAlAs/InGaAs doped channel heterostructure for high-linearity, high-temperature and high-breakdown operations

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