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     

Electron emission from direct bandgap heterojunction capacitors

The rate of emission of electrons from an inversion layer at the interface between p-type GaAs and undoped Al_xGa_1-xAs (x=0.38) is measured using a transient capacitance technique at temperatures from 49.8 to 84.4 K and at various gate biases. A model based on physical mechanisms is developed that accurately describes the inversion charge leakage. The model parameters are adjusted within their limits of uncertainty to obtain the optimal fit of present theory to experiment. The fit results in estimation of δE_c=0.28 eV and tunneling effective mass m*=0.08 m^O, for Al_0.38 Ga_0.62As. The model is used to predict the storage characteristics of similar devices with lower GaAs doping and with an alternate barrier material     

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     

Gate-length dependence of DC and microwave properties ofsubmicrometer In0.53Ga0.47As HIGFETs

In_0.52Al_0.48As/In_0.53Ga_0.47 As/InP heterostructure insulated-gate field-effect transistors (HIGFETs) with gate lengths from 1.1 and 0.3 μm have been fabricated, and their electrical performance is characterized at DC and microwave frequencies. The refractory-gate self-aligned process, applied to devices with In_0.53Ga_0.47As channels, yields an unprecedented combination of very-high speed and excellent uniformity. HIGFETs with L_g=0.6 μm showed average peak transconductance g_m of 528 mS/mm and unity-current-gain cutoff frequency f_t of 50 GHz. The uniformity of g_m was better than 1%, and the voltage of the g_m peak was uniform to ±30 mV. HIGFETs with L_g=0.3 μm showed f₁ up to 63 GHz, but suffered from serious short-channel effect, due to excessive thickness of the InGaAs channel layer. A self-aligned technique for gate resistance reduction is shown to substantially improve microwave power gain     

In0.5(AlxGa1-x)0.5HEMTs for high-efficiency low-voltage power amplifiers: design,fabrication, and device results

In_0.5(Al_xGa_1-x)_0.5 high electron-mobility transistors (HEMTs) are expected to have higher two-dimensional electron gas density and larger current drive capability than both Al_0.23Ga_0.77As and In_0.5Ga _0.5P HEMTs due to the improved conduction-band offsets. In this paper, we performed a systematic investigation of the electrical properties of In_0.5(Al_xGa_1-x)_0.5 P (0⩽x⩽1) material system lattice matched to GaAs. By considering the conduction-band offset, direct-to-indirect-band electron transfer, donor-related deep levels, and Schottky barrier height, a relatively narrow range of the Al content 0.2⩽x⩽0.3 was found to be the optimum for the design of In_0.5(Al_xGa_1-x)_0.5 HEMTs. Under 1.2-V operation, power transistors with the optimum aluminum composition show high drain current density, high transconductance, and excellent power-added efficiency (65.2% at 850 MHz). These results demonstrate that InAlGaP HEMTs are promising candidates for high-efficiency low-voltage power applications     

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     

Effect of hot-electron injection of high-frequency characteristicsof abrupt In0.52(Ga1-xAlx)0.48As/InGaAs HBT's

The effect of hot-electron injection energy (E_i) into the base on the high-frequency characteristics of In_0/52(Ga_1-xAl_x)_0.48 As/InGaAs abrupt heterojunction bipolar transistors (HBTs) is investigated by changing the composition of the emitter. There exists an optimum E_i at which a maximum current gain cutoff frequency (ft) is obtained. Analysis of hot-electron transport in the base and collector by Monte Carlo simulation is carried out to understand the above phenomenon. The collector transit time (τ_c ) increases with E_i, because electrons with higher energy transfer from the Γ valley into the upper L and X valleys. At first, the base transit time (τ_b ) decreases with E_i at the low E_i region. However, τ_b does not decrease monotically with E_i, because of the nonparabolicity in the energy-band structure of InGaAs. Consequently, there exists a minimum in the sum of τ_b and τ_c , in other words a maximum f_t, at an intermediate value of E_i     

Doubly strainedIn0.41Al0.59As/n+-In0.65Ga0.35As HFET with high breakdown voltage

An In_0.41Al_0.59As/n⁺-In_0.65 Ga_0.35As HFET on InP was designed and fabricated, using the following methodology to enhance device breakdown: a quantum-well channel to introduce electron quantization and increase the effective channel bandgap, a strained In_0.41Al_0.59As insulator, and the elimination of parasitic mesa-sidewall gate leakage. The In_0.65Ga_0.35As channel is optimally doped to N_D=6×10¹⁸ cm^-3. The resulting device (L_g=1.9 μm, W_g =200 μm) has f_t=14.9 GHz, f_max in the range of 85 to 101 GHz, MSG=17.6 dB at 12 GHz V_B=12.8 V, and I_D(max)=302 mA/mm. This structure offers the promise of high-voltage applications at high frequencies on InP     

Temperature dependence of common-emitter I-V andcollector breakdown voltage characteristics in AlGaAs/GaAs andAlInAs/GaInAs HBT's grown by MBE

Temperature-dependent measurements from 25 to 125°C have been made of the DC I-V characteristics of HBTs with GaAs and In_0.53Ga_0.47As collector regions. It was found that the GaAs HBTs have very low output conductance and high collector breakdown voltage BV_CEO>10 V at 25°C, which increases with temperature. In striking contrast, the In_0.53Ga_0.47As HBTs have very high output conductance and low BV_CEO~2.5 V at 25°C, which actually decreases with temperature. This different behavior is explained by the >10⁴ higher collector leakage current, I_CO, in In_0.53Ga_0.47As compared to GaAs due to bandgap differences. It is also shown that device self-heating plays a role in the I-V characteristics     

An improved heterostructure-emitter bipolar transistor (HEBT)

An N-Al_0.5Ga_0.5As/n-GaAs heterostructure-emitter bipolar transistor (HEBT), grown by MBE, has been fabricated with improved performance. The Al_0.5Ga_0.5As layer with higher valence-band offset ΔE_v offers better confinement of minority carriers (holes). A small offset voltage of about 80 mV and a high common-emitter current gain of 180 were measured for large-area devices. On the other hand, the adequate design of an n-GaAs emitter layer also plays an important role in device performance. The strongly knee-shaped characteristics and reachthrough effect were observed in those devices fabricated with 12 a thin n-GaAs emitter layer     

The influence of gate-feeder/mesa-edge contacting on sidegatingeffects in In0.52Al0.48As/In0.53Ga0.47As heterostructure FET's

Sidegating effects in InAlAs/InGaAs heterostructure field effect transistors (HFETs) were experimentally investigated. Two different configurations of gate feeder across the mesa edges are compared in In _0.52Al_0.48As/In_0.53Ga_0.47As. HFETs. HEMTs and heterostructure insulated-gate FETs (HIGFETs) were fabricated, each with different gate-feeder configurations. HFETs with the gate air bridge over the mesa edge can maintain 99% of the drain-source (I_ds) current level at sidegate voltages (V_sg) extending up to -30 V, while the non-air-bridge configuration of HFETs show a 30% drop of I_ds at the same V _sg. This significant discrepancy of sidegating effect is attributed to depletion region modulation at the mesa edge below the gate feeder. By lifting the gate feeder above the mesa step, sidegating is reduced, which suggests the channel/substrate trap effects are negligibly small. The role of air-bridge structures in determining the sidegating characteristics is discussed     

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     

Superposed multiquantum barriers for InGaAlP heterojunctions

In a visible-light laser using In_0.5(Ga_1-xAl _x)_0.5P (0⩽x⩽1), the conduction-band discontinuity at the interface between the active layer and clad layer is not large enough to strongly suppress carriers overflowing into the clad layer, unlike in the GaAlAs system. A multiquantum barrier (MQB) is used to overcome this problem, and the electron-reflecting powers are calculated to determine the characteristics of this suppression. Electron-reflecting powers are calculated for a high-power, high-temperature laser with an In_0.5 Ga_0.5P active layer, an In_0.5Ga_0.15 clad layer, and a set of superposed MQBs, and for a short-wavelength (λ:586-nm) laser composed of an In_0.5Ga_0.33Al_0.17P active layer, an In _0.5Ga_0.15Al_0.35P clad layer, and a set of superposed MQBs     

Electrical and optical properties of deep-red top-surface-emittinglasers

By studying thermal behavior of all-MBE surface-emitting lasers, barrier heights and optimum cavity design parameters are obtained. The barrier heights for holes between hetero-interfaces of Al_0.3Ga_0.7As-Al_0.65Ga_0.35As and AlAs-Al_0.65Ga_0.35As (Δx=-0.35) are measured to be 77 meV at zero bias for the deep-red top-surface-emitting laser. The barrier height decreases linearly with forward bias voltage, explaining the nonlinearity in current-voltage characteristics of the top-surface-emitting laser. The contribution of electrons to electrical resistance is estimated to be negligibly small compared to that of holes for the structure consisting of Δ_x =0.35. Minimum threshold current and maximum differential quantum efficiency observed around 200 K indicate slight mismatch between gain maximum and Fabry-Perot resonance for the deep-red top-surface-emitting laser     

A Two-Step-Recess Process Based on Atomic-Layer Etching for High-Performance $hbox{In}_{0.52}hbox{Al}_{0.48}hbox{As}hbox{/}hbox{In}_{0.53} hbox{Ga}_{0.47}hbox{As}$ p-HEMTs

We investigated 60-nm In_0.52Al_0.48As/In_0.53Ga_0.47As pseudomorphic high-electron mobility transistors (p-HEMTs) fabricated by using a Ne-based atomic-layer-etching (ALET) technology. The ALET process produced a reproducible etch rate of 1.47 Aring/cycle for an InP etch stop layer, an excellent InP etch selectivity of 70 against an In_0.52Al_0.48As barrier layer, and an rms surface-roughness value of 1.37 Aring for the exposed In_0.52Al_0.48As barrier after removing the InP etch stop layer. The application of the ALET technology for the gate recess of 60-nm In_0.52Al_0.48As/In_0.53Ga_0.47As p-HEMTs produced improved device parameters, including transconductance (G_M), cutoff frequencies (f_T)> and electron saturation velocity (vsat) in the channel layer, which is mainly due to the high etch selectivity and low plasma-induced damage to the gate area. The 60-nm In_0.52Al_0.48As/In_0.53Ga_0.47As p-HEMTs fabricated by using the ALET technology exhibited G_M,_Max = 1-17 S/mm, f_T = 398 GHz, and v_sat = 2.5 X 10⁷ cm/s.     

Logic Suitability of 50-nm In0.7 Ga0.3As HEMTs for Beyond-CMOS Applications

We have experimentally studied the suitability of nanometer-scale In_0.7Ga_0.3As high-electron mobility transistors (HEMTs) as an n-channel device for a future high-speed and low-power logic technology for beyond-CMOS applications. To this end, we have fabricated 50- to 150-nm gate-length In_0.7Ga_0.3As HEMTs with different gate stack designs. This has allowed us to investigate the role of Schottky barrier height (Phi_B) and insulator thickness (t_ins) on the logic characteristics of In_0.7Ga_0.3As HEMTs. The best 50-nm HEMTs with the highest Phi_B and the smallest t_ins exhibit an I_ON/I_OFF ratio in excess of 10⁴ and a subthreshold slope (S) below 86 mV/dec. These nonoptimized 50-nm In_0.7Ga_0.3As HEMTs also show a logic gate delay (CV/I) of around 1 ps at a supply voltage of 0.5 V, while maintaining an I_ON/I_OFF ratio above 10⁴, which is comparable to state-of-the-art Si MOSFETs. As one of the alternatives for beyond-CMOS technologies, we believe that InAs-rich InGaAs HEMTs hold a considerable promise.     

8-element linear array monolithic p-i-n MODFET photoreceivers usingmolecular beam epitaxial regrowth

An 8-element linear array of single-stage integrating front-end photoreceivers using molecular beam epitaxial (MBE) regrowth was investigated. Each element consisted of a p-i-n In_0.53Ga_0.47As photodiode integrated with a selectively regrown pseudomorphic In_0.65Ga_0.35As/In_0.52Al_0.48 As MODFET. Cutoff frequencies of 1.0-μm discrete regrown MODFETs were f_t=24 GHz and f_max=50 GHz. Transconductance of the regrown MODFETs was as high as 495 mS/mm with a current density (I_ds) of 250 mA/mm. The 3-dB bandwidth of the photoreceiver was measured to be 1 GHz. The bit rate sensitivity at 1 Gb/s was -31.8 dBm for BER 10^-9 using 1.55 μm excitation for a photoreceiver with an anti-reflection coating. The single-stage amplifier exhibited up to 25 dB flatband gain of the photocurrent, and a two-stage amplifier was up to 31 dB of gain. Good uniformity between each photoreceiver element in the array was achieved. Electrical crosstalk between photoreceiver elements was estimated to be ~-34 dB     

Polarization-independent strained InGaAs/InGaAlAs quantum-wellphase modulators

Polarization-independent phase modulation in In_1-xGa _xAs/InGaAlAs multiple-quantum-well waveguides is demonstrated for the first time. It is shown that by increasing the Ga fraction and hence the tensile strain in the quantum well the electric-field-induced refractive index change in the TM polarization Δn_TM can be made to approach that in the TE polarization Δn _TE. At 1.523 μm, the ratio Δn_TM /Δn_TE=1 for x=0.7 with a phase shift coefficient of 17.4°/V-mm was achieved. Polarization independence was maintained over the entire range of reverse bias voltage     

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     

Monte Carlo study of GaAs/Alx Ga1-xAsMODFETs: effects of AlxGa1-xAs composition

Monte Carlo methods are used to compare electronic transport and device behavior in n⁺-Al_xGa_1-xAs/GaAs modulation-doped field-effect transistors (MODFETs) at 300 K for x =0.10, 0.15, 0.22, 0.30, 0.35, and 0.40. The differences between the x=0.22 and x=0.30 MODFETs with respect to parasitic conduction in Al_xGa_1-xAs, gate currents, and switching times, are of particular interest. The donor-related deep levels in Al_xGa_1-xAs, are disregarded by assuming all donors to be fully ionized, and the focus is only on the confinement and transport of the carriers. The following quantities are studied in detail: transfer characteristics (I_D versus V _G), transconductance (g_m), switching speeds (τ_ON), parasitic conduction in Al_xGa _1-xAs, gate current (I_G), average electron velocities and energies in GaAs and Al_xGa_1-x As, electron concentration in the device domain, k-space transfer (to low mobility L and X valleys), and details of the real-space transfer process