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     

Highly strained InGaP/InGaAs p-HEMT using reduced area growth

Highly strained InGaP/In_0.33Ga_0.67As pseudomorphic high electron mobility transistor (p-HEMT) structures were grown on patterned GaAs substrates. Performance of the highly strained p-HEMTs grown on patterned substrates was compared with that of highly strained p-HEMTs and conventional InGaP/In_0.22Ga_0.78 As p-HEMTs grown on nonpatterned substrates. The highly strained p-HEMTs grown on patterned substrates showed substantial improvements in dc (transconductance and drain saturation current) and rf (cutoff frequency: f_T and maximum oscillation frequency: f_max ) performances as compared with those of the p-HEMTs grown on nonpatterned substrates. The results indicate the potential of highly strained p-HEMTs using reduced area growth for high-speed device applications     

High-performance In0.08Ga0.92As MESFETs onGaAs(100) substrates

In_0.08Ga_0.92As MESFETs were grown in GaAs (100) substrates by molecular beam epitaxy (MBE). The structure comprised an undoped compositionally graded In_xGa_1-x As buffer layer, an In_0.08Ga_0.92As active layer, and an n⁺-In_0.08Ga_0.92As cap layer. FETs with 50-μm width and 0.4-μm gate length were fabricated using the standard processing technique. The best device showed a maximum current density of 700 mA/mm and a transconductance of 400 mS/mm. The transconductance is extremely high for the doping level used and is comparable to that of a 0.25-μm gate GaAs MESFET with an active layer doped to 10¹⁸ cm^-3. The current-gain cutoff frequency was 36 GHz and the power-gain cutoff frequency was 65 GHz. The current gain cutoff frequency is comparable to that of a 0.25-μm gate GaAs MESFET     

Is the be incorporation the same in (311)A and (100) AlGaAs?

The incorporation of the Be acceptor in Al_xGa_{1 − x}As grown by molecular beam epitaxy on (100) and (311)A oriented substrates is investigated by photoluminescence and electrical measurements. Values of the Be binding energy slightly lower than the commonly accepted ones have been found: 32 ± 4 meV at x 0.24. The incorporation efficiency is slightly greater in (311)A than in (100) oriented AI_xGa_{1 − x}As. The Be doping of (311)A oriented AI_x-Ga_{1 − x}As produces materials of higher electrical and optical properties than the Be doping of (100) oriented Al_xGa_{1 − x}As.     

High performance pseudomorphic InGaP/InGaAs power HEMTs

Power transistors with a low d.c. supply voltage were demonstrated with pseudomorphic InGaP/In_0.2Ga_0.8As/GaAs heterostructure field effect transistors on GaAs substrates and 1 μm gate length technology. A current density of 200 mA mm⁻¹ and an extrinsic transconductance of 300 mS mm⁻¹ were exhibited on a 400 μm gate width process control monitor device. For a 1 cm gate width device measured at 850 MHz and V_ds = 1.3 V, state-of-the-art results, 57.4% for the PAE, 12.7 dB for the linear gain and 21.5 dBm for the output power, were obtained.     

Low-temperature microwave characteristics of pseudomorphic InxGa1-xAs/In0.52Al0.48Asmodulation-doped field-effect transistors

Low-temperature microwave measurements of both lattice-matched and pseudomorphic In_xGa_1-xAs/In_0.48As (x=0.53, 0.60, and 0.70) channel MODFETs on InP substrates were carried out in a cryogenic measurement system. The measurements were done in the temperature range of 77 to 300 K and in the frequency range of 0.5 to 11.0 GHz at different bias conditions. The cutoff frequency ( f_T) for the In_xGa_1-xAs/In_0.52Al_0.48As MODFETs improved from 22 to 29 GHz, 29 to 38 GHz, and 39 to 51 GHz, for x=0.53, 0.60, and 0.70, respectively, as the temperature was lowered from 300 to 77 K, which is approximately a 31% increase at each composition. No degradations were observed in device performance. These results indicate an excellent potential of the pseudomorphic devices at low temperatures     

Piezoelectric field measurements by photoreflectance in strained InGaAs/GaAs structures grown on polar substrates

Photoreflectance (PR) measurements were performed on specific structures grown by molecular-beam epitaxy on different substrate orientations: 111B, 111B 2° off, 111A and 100. A strained In_0.2Ga_0.8As quantum well was grown in the space charge layer of an undoped GaAs layer. On a polar substrate orientation 111, the strain-induced piezoelectric field in the quantum well modifies the field in the space charge layer. PR spectra recorded in such structures exhibit Franz Keldysh oscillations from which we can measure the internal electric field. The piezoelectric field is then deduced from a comparison between two structures differing only by the presence of the strained quantum well. Experimental values ranged between 110 kV/cm and 150 kV/cm, and were used to determine experimentally the piezoelectric constant e₁₄ in In_0.2Ga_0.8As.     

InGaP/InGaAs HFET with high current density and high cut-offfrequencies

Doped channel pseudomorphic In_0.49Ga_0.51P/In _0.20Ga_0.80As/GaAs heterostructure field effect transistors have been fabricated on GaAs substrate with 0.25 μm T-gates and self-aligned ohmic contact enhancement. By introducing the channel doping and reducing the series resistances, a high current density of 500 mA/mm is obtained in combination with cut off frequencies of f_T=68 GHz and f_max=160 GHz. The channel doping did not affect the RF-performance of the device essentially, which is additionally reflected in noise figures below 1.0 dB with an associated gain of 14.5 dB at 12 GHz     

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     

Millimeter-wave ion-implanted gradedInxGa1-xAs MESFETs grown by MOCVD

The authors present the fabrication and characterization of ion-implanted graded In_xGa_1-xAs/GaAs MESFETs. The In_xGa_1-xAs layers are grown on GaAs substrates by MOCVD (metal-organic chemical vapor deposition) with InAs concentration graded from 15% at the substrate to 0% at the surface. 0.5-μm gate MESFETs are fabricated on these wafers using silicon ion implantation. In addition to improved Schottky contact, the graded In_xGa _1-xAs MESFET achieves maximum extrinsic transconductance of 460 mS/mm and a current-gain cutoff frequency f_t of 61 GHz, which is the highest ever reported for a 0.5-μm gate MESFET. In comparison, In_0.1Ga_0.9As MESFETs fabricated with the same processing technique show an f_t of 55 GHz     

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     

Molecular beam epitaxial GaAs/Al0.2Ga0.8Asp-channel field-effect transistors on (311)A facets of patterned (100)GaAs obtained by silicon doping

P-channel and n-channel heterostructure field effect transistors (HFETs) have been simultaneously fabricated by one-step molecular beam epitaxial growth of Si-doped Al_0.2Ga_0.8As/GaAs heterostructures on patterned (100) GaAs substrates. The p-HFETs were made on the etched (311)A facets and the n-HFETs on the planar (100) surface. A transconductance value of 23 mS/mm at 300 K for a p-HFET with a 1.1×50-μm gate is measured. The same size n-HFET made with the same structure and same level of Si doping has a transconductance value of 250 mS/mm at room temperature     

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     

High peak-to-valley current ratioIn0.22Ga0.78As/AlAs RTDs on GaAs using relaxed InxGa1-x buffers

The authors have grown In_0.22Ga_0.78As/AlAs resonant tunnelling diodes (RTDs) on relaxed In_xGa_1-x As buffers on GaAs substrates, which show the largest peak-to-valley current ratio (PVCR), 13:1, ever reported for GaAs-based RTDs. X-ray diffraction and photoluminescence (PL) studies confirm the composition and relaxation of the buffers. The intrinsic device performance is excellent despite the presence of some dislocations in the active layers. However, it appears that the relaxed buffers do add series resistance to the intrinsic device     

Ga0.51In0.49P/In0.15Ga0.85As/GaAs pseudomorphic doped-channel FET with high-current densityand high-breakdown voltage

Ga_0.51In_0.49P/In_0.15Ga_0.85 As/GaAs pseudomorphic doped-channel FETs exhibiting excellent DC and microwave characteristics were successfully fabricated. A high peak transconductance of 350 mS/mm, a high gate-drain breakdown voltage of 31 V and a high maximum current density (575 mA/mm) were achieved. These results demonstrate that high transconductance and high breakdown voltage could be attained by using In_0.15Ga_0.85As and Ga_0.51In_0.49P as the channel and insulator materials, respectively. We also measured a high-current gain cut-off frequency f_t of 23.3 GHz and a high maximum oscillation frequency f_max of 50.8 GHz for a 1-μm gate length device at 300 K. RF values where higher than those of other works of InGaAs channel pseudomorphic doped-channel FETs (DCFETs), high electron mobility transistors (HEMTs), and heterostructure FETs (HFETs) with the same gate length and were mainly attributed to higher transconductance due to higher mobility, while the DC values were comparable with the other works. The above results suggested that Ga_0.51In_0.49P/In_0.15Ga_0.85 As/GaAs doped channel FET's were were very suitable for microwave high power device application     

Metamorphic InP/InGaAs heterojunction bipolar transistors on GaAssubstrate: DC and microwave performances

High-performance InP/In_0.53Ga_0.47As metamorphic heterojunction bipolar transistors (MHBTs) on GaAs substrate have been fabricated using In_xGa_1-xP strain relief buffer layer grown by solid-source molecular beam epitaxy (SSMBE). The MHBTs exhibited a dc current gain over 100, a unity current gain cutoff frequency (f_T) of 48 GHz and a maximum oscillation frequency (f_MAX) of 42 GHz with low junction leakage current and high breakdown voltages. It has also been shown that the MHBTs have achieved a minimum noise figure of 2 dB at 2 GHz (devices with 5×5 μm ² emitter) and a maximum output power of 18 dBm at 2.5 GHz (devices with 5×20 μm² emitter), which are comparable to the values reported on the lattice-matched HBTs (LHBTs). The dc and microwave characteristics show the great potential of the InP/InGaAs MHBTs on GaAs substrate for high-frequency and high-speed applications     

Influence of pseudomorphic base-emitter spacer layers oncurrent-induced degradation of beryllium-doped InGaAs/InAlAsheterojunction bipolar transistors

We present in this paper a basis for the design of high performance heterojunction bipolar transistors in which base dopant diffusion can be drastically reduced, or even eliminated. From previous theoretical and experimental studies we have established that the motion of point defects in a semiconductor can be impeded or enhanced by a thin (30-100 Å) pseudomorphic layer. The path preferred by the defect will depend on the local strain exerted by it in the lattice and the strain tensor of the host layer. Based on this, we have studied the outdiffusion of Be dopant atoms from the base region of n-p-n In_0.53Ga_0.47As/In_0.52Al_0.48 As heterojunction bipolar transistors (HBT's) during short-term high-current (t=18-24 h, J_c=7×10⁴ A/cm² , T=80°C) stress tests. The microwave transistors grown by molecular beam epitaxy have 150-200 Å of lattice-matched, compressively strained, or tensilely strained spacer layers incorporated between the base and emitter layers. Changes are observed in the dc and microwave characteristics of the transistors with lattice-matched and compressively strained spacers, while no changes are recorded in the devices with tensilely strained spacer layer after the current stress test. As expected, the tensiley strained spacer layer is very effective in controlling the outdiffusion of Be dopant atoms, which exert a local strain in the lattice, from the base to the emitter region     

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     

Quantum-well Hall devices in Si-delta-dopedAl0.25Ga0.75As/GaAs and pseudomorphic Al0.25Ga0.75As/In0.25Ga0.75As/GaAsheterostructures grown by LP-MOCVD: performance comparisons

Characterized herein are quantum-well Hall devices in Si-delta-doped Al_0.25Ga_0.75As/GaAs and pseudomorphic Al_0.25Ga_0.75As/In_0.25Ga _0.75As/GaAs heterostructures, grown by low-pressure metal organic chemical vapor deposition method. The Si-delta-doping technique has been applied to quantum-well Hall devices for the first time. As a result high electron mobilities of 8100 cm^-2/V·s with a sheet electron density of 1.5×10¹² cm^-2 in Al_0.25Ga_0.75As/In_0.25Ga_0.75 As/GaAs structure and of 6000 cm^-2/V·s with the sheet electron density of 1.2×10¹² cm^-2 in Al_0.25Ga_0.75As/GaAs structure have been achieved at room temperature, respectively. From Hall devices in Al_0.25Ga_0.75As/In_0.25Ga_0.75 As structure, the product sensitivity of 420 V/AT with temperature coefficient of -0.015 %/K has been obtained. This temperature characteristic is one of the best result reported. Additionally, a high signal-to-noise ratio corresponding to the minimum detectable magnetic field of 45 nT at 1 kHz and 75 nT at 100 Hz has been attained. These resolutions are among the best reported results     

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