In0.52Al0.48As/In0.53Ga0.47As MSM photodetectors and HEMT's grown by MOCVD on GaAs substrates

The authors report the first demonstration of In_0.52Al _0.48As/In_0.53Ga_0.47As metal-semiconductor-metal (MSM) photodetectors and high-electron-mobility transistors (HEMTs) grown on GaAs substrates by organometallic chemical vapor deposition. Both photodetectors and transistors showed no degradation in performance compared to devices simultaneously grown on InP substrates. The photodetectors exhibited a responsivity of 0.45 A/W and leakage current of 10 to 50 nA. The HEMTs with a gate length of 1.0 μm showed a transconductance as high as 250 mS/mm, and f_T and f_max of 25 and 70 GHz, respectively     

High-performance back-illuminated InGaAs/InAlAs MSM photodetectorwith a record responsivity of 0.96 A/W

A high-performance back-illuminated In_0.53Ga_0.47 As/In_0.52Al_0.48As/InP metal-semiconductor-metal (MSM) detector is reported. A record responsivity of 0.96 A/W at 1.3-μm wavelength, corresponding to a quantum efficiency of 92%, was measured at 5 V and showed virtually no internal gain at 20 V. Packaged devices with 150-μm-diameter large detection area showed a 3-dB bandwidth of 4 GHz at 5 V with fiber pigtail butt-coupled package and 3.5 GHz with fiber pigtail silicon V-grooved package. Switching to front-illumination improves the bandwidth by 30-40% with 45-50% reduction of responsivity. Planar and mesa devices both show a low capacitance per unit area of 3.0 nF/cm² and dark current density of 5.6×10^-5 A/cm² at 5 V. Preliminary reliability test results show that the detector biased at 5 V survived temperature cycling of -35°C to 200°C, high-temperature burn-in at 125°C for 168 h and subsequent short-term accelerated aging at 200°C for 120 h without degradation     

In0.53Ga0.47As MSM photodiodes withtransparent CTO Schottky contacts and digital superlattice grading

Metal-semiconductor-metal (MSM) photodiodes with an In_0.53 Ga_0.47As active region were investigated using a transparent cadmium tin oxide (CTO) layer for the interdigitated electrodes to improve the low responsivity of conventional MSM photodiodes with opaque electrodes. CTO is suitable as a Schottky contact, an optical window and an anti-reflection (AR) coating. The transparent contact prevents shadowing of the active layer by the top electrode, thus allowing greater collection of incident light. Responsivity of CTO-based MSM photodiodes with 1-μm finger widths and 2-μm finger spacings and without an AR coating between the electrodes was twice (0.62 A/W) that of a similar MSM photodiodes with Ti/Au electrodes (0.30 A/W). A thin 800 Å In_0.52Al_0.48 As layer was inserted below the electrodes to elevate the electrode Schottky barrier height. A digitally graded superlattice region (660 A) was also employed to reduce carrier trapping at the In _0.53Ga_0.47As/In_0.52Al_0.48As heterointerface which acts to degrade photodiode bandwidth. Bandwidth of opaque electrode MSMs was elevated nearly an order of magnitude over a previous MSM photodiode design with an abrupt heterointerface, whereas the bandwidth of transparent electrode MSM's only improved about five times, indicating resistive effects may be intervening     

Long-wavelength In0.53Ga0.47As metamorphicp-i-n photodiodes on GaAs substrates

Metamorphic In_0.53Ga_0.47As p-i-n photodiodes on GaAs substrate exhibiting the lowest dark current ever reported were fabricated and characterized. Their dark current, DC and RF performances were measured and compared for devices of different sizes. Typical dark current for 15-μm-diameter devices was 600 pA under 5-V reverse bias, corresponding to a dark current density of 3.40×10^-4 A/cm². Typical responsivity measured with 1.55-μm optical radiation was 0.55 A/W corresponding to an external quantum efficiency of 44%. The electrical 3 dB bandwidths of the photodiodes with diameters smaller than 20 μm were over 20 GHz     

High-performance undoped InP/n-In0.53Ga0.47AsMSM photodetectors grown by LP-MOVPE

A new high-performance undoped In_0.53Ga_0.47As metal-semiconductor-metal photodetector (MSM-PD) with an undoped InP barrier-enhancement layer is reported. The layers were grown by the low-pressure metalorganic vapor-phase epitaxy (LP-MOVPE) technique. The main features of this device include: a very low dark current of less than 60 nA, (100×100) μm², at 1.5 V; a short risetime of 30 ps at 6 V; and a high responsivity of 0.42 A/W for λ=1.3 μm     

In0.52Al0.48As/In0.53Ga0.47As double-heterojunction p-n-p bipolar transistors grown bymolecular beam epitaxy

P-n-p In_0.52Al_0.48As/In_0.53Ga_0.47 As double-heterojunction bipolar transistors with a p⁺-InAs emitter cap layer grown by molecular-beam epitaxy have been realized and tested. A five-period 15-Å-thick In_0.53Ga_0.47As/InAs superlattice was incorporated between the In_0.53Ga_0.47As and InAs cap layer to smooth out the valence-band discontinuity. Specific contact resistance of 1×10^-5 and 2×10^-6 Ω-cm² were measured for nonalloyed emitter and base contacts, respectively. A maximum common emitter current gain of 70 has been measured for a 1500-Å-thick base transistor at a collector current density of 1.2×10³ A/cm². Typical current gains of devices with 50×50-μm² emitter areas were around 50 with ideality factors of 1.4     

0.12 μm transferred-substrateIn0.52Al0.48As/In0.53Ga0.47As HEMTs on silicon wafer

New In_0.52Al_0.48As/In_0.53Ga_0.47 As transferred-substrate high electron mobility transistors (TS-HEMTs) have been successfully fabricated on 2-in Silicon substrate with 0.12 μm T-shaped gate length. These new TS-HEMTs exhibit typical drain currents of 450 mA/mm and extrinsic transconductance up to 770 mS/mm. An extrinsic current gain cutoff frequency f_T of 185 GHz is obtained. That result is the first reported for In_0.52Al_0.48As/In_0.53Ga_0.47 As TS-HEMTs on Silicon substrate     

Self-alignedIn0.52Al0.48As/In0.53Ga0.47As heterojunction bipolar transistors with graded interface onsemi-insulating InP grown by molecular beam epitaxy

A self aligned In_0.52Al_0.48As/In_0.53 Ga_0.47As double heterojunction bipolar transistor (HBT) with a graded heterointerface has been grown by molecular-beam epitaxy (MBE) and tested. The DC characteristics of HBT structures with a compositionally graded junction using a linear graded In_0.53Ga_0.47-xAl_xAs between two ternary layers were investigated. Typical quaternary graded devices with an emitter dimension of 50×50 μm² exhibited a current gain as high as 1260, as compared to 800 for abrupt devices, at a collector current density of 2.8×10³ A/cm²     

Metamorphic In0.4Al0.6As/In0.4Ga0.6As HEMTs on GaAs substrate

New In_0.4Al_0.6As/In_0.4Ga_0.6 As metamorphic (MM) high electron mobility transistors (HEMTs) have been successfully fabricated on GaAs substrate with T-shaped gate lengths varying from 0.1 to 0.25 μm. The Schottky characteristics are a forward turn-on voltage of 0.7 V and a gate breakdown voltage of -10.5 V. These new MM-HEMTs exhibit typical drain currents of 600 mA/mm and extrinsic transconductance superior to 720 mS/mm. An extrinsic current cutoff frequency f_T of 195 GHz is achieved with the 0.1-μm gate length device. These results are the first reported for In_0.4 Al_0.6As/In_0.4Ga_0.6As MM-HEMTs on GaAs substrate     

Electrical characteristics of an optically controlled N-channelAlGaAs/GaAs/InGaAs pseudomorphic HEMT

Electrical characteristics of an n-channel Al_0.3Ga_0.7As/GaAs/In_0.13Ga_0.87 As pseudomorphic HEMT (PHEMT) with L_g=1 μm on GaAs are characterized under optical input (P_opt). Gate leakage and drain current have been analyzed as a function of V_GS, V _DS, and P_opt. We observed monotonically increasing gate leakage current due to the energy barrier lowering by the optically induced photovoltage, which means that gate input characteristics are significantly limited by the photovoltaic effect. However, we obtained a strong nonlinear photoresponsivity of the drain current, which is limited by the photoconductive effect. We also proposed a device model with an optically induced parasitic Al_0.3Ga_0.7As MESFET parallel to the In_0.13Ga_0.87As channel PHEMT for the physical mechanism in the drain current saturation under high optical input power     

InP/In0.53Ga0.47As heterojunction bipolartransistors with a carbon-doped base grown by MOCVD

InP/In_0.53Ga_0.47As heterojunction bipolar transistors (HBTs) utilizing a carbon-doped base have been demonstrated. The devices were grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) using carbon tetrachloride (CCl₄) as the p-type dopant source. These devices exhibit a DC common-emitter current gain of 50 and an emitter-base junction ideality factor of 1.29 in a structure for which no undoped spacer layer was employed at the emitter-base junction. These preliminary results suggest that C-doping of In_0.53Ga_0.47As may be a suitable alternative to Zn in MOCVD-grown InP/In_0.53Ga_0.47As HBTs     

Theoretical analysis of the influences of barrier-enhancementlayers on transient responses of MSM photodetectors

Transient responses of In_0.53Ga_0.47As MSM PDs with abrupt and graded barrier-enhancement layers are simulated by using an ensemble Monte Carlo technique. The effect of the graded layer on transient responses and an appropriate graded-layer thickness for achieving fast responses are discussed. Also, a relevant device scaling law is proposed for In_0.53Ga_0.,₄₇As MSM PDs with graded barrier-enhancement layers     

Low temperature microwave characteristics of 0.1 μm gate-lengthpseudomorphicIn0.52Al0.48As/InxGa1-xAs(x=0.85 and 0.95) MODFET's

We have studied the microwave characteristics of 0.1 μm gate-length pseudomorphic In_0.52Al_0.48As/In_x Ga_1-xAs (x=0.85 and 0.95) modulation-doped field-effect transistors (MODFET's) at 300 K and lower temperatures down to 77 K. A maximum f_T of 151 GHz has been measured for a 0.1×55 μm² gate In_0.52Al_0.48As/In_0.85 Ga_0.15As MODFET at 77 K and this represents an improvement of 33% over the room temperature value. This behavior has been analyzed     

In0.52Al0.48As/InAs/InxAl1-xAs pseudomorphic HEMT's on InP

The DC and microwave performance of an InAs channel HEMT is reported. Room-temperature electron mobility as high as 20200 cm² /Vs is measured, with a high carrier concentration of 2.7×10 ¹² cm^-2. DC extrinsic transconductance of 714 mS/mm is measured and a unity-current-gain cut-off frequency of 50 GHz is obtained for a 1.1-μm gate length HEMT. The success of achieving superior Hall mobility and device performance is strongly dependent on the In_xAl_1-xAs buffer layer design that changes the lattice constant from lattice-matched In_0.52Al_0.48 As to In_0.75Al_0.25As. The multiple In_0.52Al_0.48As/InAs monolayer superlattices buffer achieves the best performance as compared to the step-graded In_x Al_1-xAs and the uniform In_0.76Al_0.25 As buffer     

DC and microwave characteristics of InAlAs/InGaAssingle-quantum-well MODFETs with GaAs gate barriers

The design and performance of In_0.53Ga_0.47As/In_0.52Al_0.48 As modulation-doped field-effect transistors (MODFETs) have been optimized by incorporating a single In_0.53Ga_0.47As quantum-well channel and a thin strained GaAs gate barrier layer. These help to lower the output conductance and gate leakage current of the device, respectively. The DC performance of 1-μm-gate devices is characterized by extrinsic transconductances of 320 mS/mm at 300 K and 450 mS/mm at 77 K and a best value of f_T=35 GHz is derived from S-parameter measurements     

Dark current analysis and characterization ofInxGa1-xAs/InAsyP1-y gradedphotodiodes with x>0.53 for response to longer wavelengths(>1.7 μm)

The dark current properties of In_xGa_1-xAs photodiodes, where x is varied from 0.53 to 0.82 for extending the long wavelength cutoff from 1.7 to 2.6 μm, are described. Detailed analyses of optoelectrical parameters of In_0.82Ga _0.1As photodiodes are presented. Dark current, which is a critical parameter and limits the operation of the photodiode, is analyzed and compared with the experimental values. Typical characteristics of photodiodes with cutoff wavelengths of 1.7 μm (x=0.53), 2.2 μm (x=0.72), and 2.6 μm (x=0.82) are presented. The typical and best values of the dark currents obtained are presented     

Characteristics of a In0.52(AlxGa1-x)0.48As/In0.53Ga0.47As(0⩽x⩽1) heterojunction and its application onHEMT's

The quaternary In_0.52(Al_xGa_1-x) _0.48As compound on InP substrates is an important material for use in optoelectronic and microwave devices. We systematically investigated the electrical properties of quaternary In_0.52(Al_xGa_1-x)_0.48As layers, and found a 10% addition of Ga atoms into the InAlAs layer improves the Schottky diode performance. The energy bandgap (E_g ) for the In_0.52(Al_xGa_1-x)_0.48As layer was (0.806+0.711x) eV, and the associated conduction-band discontinuity (ΔE_c), in the InAlGaAs/In_0.53Ga_0.47 As heterojunction, was around (0.68±0.01)ΔE_g . Using this high quality In_0.52(Al_0.9Ga_0.1)_0.48As layer in the Schottky and buffer layers, we obtained quaternary In_0.52(Al_0.9Ga_0.1)_0.48As/In _0.53Ga_0.47As HEMTs. This quaternary HEMT revealed excellent dc and microwave characteristics. In comparison with the conventional InAlAs/InGaAs HEMT's, quaternary HEMT's demonstrated improved sidegating and device reliability     

Molecular beam epitaxy growth and characterization of InGaP/InGaAspseudomorphic high electron mobility transistors (HEMTs) having achannel layer over critical layer thickness

In_0.5Ga_0.5P/In_xGa_1-xAs (x=0.33 and 0.40), pseudomorphic high electron mobility transistors (p-HEMTs) having a channel layer over the critical layer thickness were grown on patterned and nonpatterned GaAs substrates by using a compound-source molecular beam epitaxy (MBE). Characteristics of the highly strained InGaP/In_xGa_1-xAs (x=0.33 and 0.40) p-HEMTs grown on patterned substrates were compared with those of conventional InGaP/In_0.22Ga_0.78As p-HEMTs grown on a nonpatterned substrate. The highly strained InGaP/In_0.33Ga _0.67As p-HEMT showed substantial improvements in device performances including DC (drain saturation current and transconductance), microwave (f_T and f_max), low-frequency noise (Hooge parameter), and high-frequency noise (minimum noise figure and associated gain) characteristics compared with those of the conventional InGaP/In_0.22Ga_0.78As p-HEMT. The improvements in device performances of the highly strained InGaP/In_0.33Ga_0.67As p-HEMT are attributed to the improved transport property of the high-quality highly strained In_0.33Ga_0.67As channel layer achieved by the use of the patterned substrate growth. The results indicate the potential of highly strained InGaP/In_xGa_1-xAs p-HEMTs having a channel layer in excess of the critical layer thickness grown on patterned GaAs substrates for use in high-performance microwave device applications     

0.2-μm gate-length atomic-planar doped pseudomorphic Al0.3Ga0.7As/In0.25Ga0.75As MODFETswith fT over 120 GHz

The authors report the DC and RF performance of nominally 0.2-μm-gate length atomic-planar doped pseudomorphic Al_0.3Ga_0.7As/In_0.25Ga_0.75As modulation-doped field-effect transistors (MODFETs) with f_T over 120 GHz. The devices exhibit a maximum two-dimensional electron gas (2 DEG) sheet density of 2.4×10¹² cm^-2, peak transconductance g _m of 530-570 mS/mm. maximum current density of 500-550 mA/mm, and peak current-gain cutoff frequency f_T of 110-122 GHz. These results are claimed to be among the best ever reported for pseudomorphic AlGaAs/InGaAs MODFETs and are attributed to the high 2 DEG sheet density, rather than an enhanced saturation velocity, in the In_0.25Ga_0.75As channel     

Single- and double-heterojunction pseudomorphic In0.5(Al0.3Ga0.7)0.5P/In0.2Ga0.8As high electron mobility transistors grown by gas sourcemolecular beam epitaxy

In_0.5(Al_0.3Ga_0.7)_0.5 P/In_0.2Ga_0.8As single- and double-heterojunction pseudomorphic high electron mobility transistors (SH-PHEMTs and DH-PHEMTs) on GaAs grown by gas-source molecular beam epitaxy (GSMBE) were demonstrated for the first time. SH-PHEMTs with a 1-μm gate-length showed a peak extrinsic transconductance g_m of 293 mS/mm and a full channel current density I_max of 350 mA/mm. The corresponding values of g_m and I_max were 320 mS/mm and 550 mA/mm, respectively, for the DH-PHEMTs. A short-circuit current gain (H₂₁) cutoff frequency f_T of 21 GHz and a maximum oscillation frequency f_max of 64 GHz were obtained from a 1 μm DH device. The improved device performance is attributed to the large ΔE_c provided by the In_0.5(Al_0.3Ga_0.7)_0.5P/In _0.2Ga_0.8As heterojunctions. These results demonstrated that In_0.5(Al_0.3Ga_0.7)_0.5P/In _0.2Ga_0.8As PHEMT's are promising candidates for microwave power applications