Small-signal analysis of 1.3-μm microcavity light-emittingdiodes

The modulation speed of 1.3-μm microcavity light-emitting diodes (MCLEDs) has been measured using a small-signal modulation analysis. A speed of 260 MHz using a 25-μm diameter sample at current density of 10 kA/cm² has been achieved. The carrier confinement has been calculated for several carrier densities in order to investigate the origin of the speed limitation. By comparing the performance of the 1.3-μm MCLEDs with that of the 990-nm devices we conclude that the limiting factor on the speed seems to be a lack of carrier confinement in the quantum wells and not a cavity effect     

Long-wavelength (9.5-11.5 μm) microdisk quantum-cascade lasers

Quantum-cascade whispering-gallery-mode disk lasers emitting at 9.5-μm and 11.5-μm wavelength are reported. Taking advantage of the high-quality resonator (Q≈200), the threshold current density of disk lasers emitting at 9.5 μm is reduced below the value of the corresponding ridge waveguide geometry (J_th,disk=2.39 kA.cm ^-2 versus J_th,ridge=3.0 kA.cm^-2). Additionally, the increase in wavelength compared to previously reported disk lasers at 5.0 μm is a significant step toward the microcavity regime (by an effective scaling factor of 2.5, comparing identical disk sizes), disk diameters from 125 μm down to 20 μm are used to study the approach to the microcavity regime by size reduction. Far-field pattern measurements identify scattering from the pedestal as an important outcoupling mechanism for microdisk lasers. An excellent agreement between the measured and calculated free spectral range of the whispering gallery modes allows us to estimate the beta factor of the microdisks, resulting in β≈0.05 for a 20-μm diameter disk. A two-level rate equation model is evaluated for the quantum-cascade disk laser as a tool for a direct measurement of β. Nevertheless, the actual measurement is at present blurred by luminescence (light-emitting diode) from the disk center accompanied by an unbalanced carrier distribution between the whispering gallery laser and the center light-emitting diode     

High-performance long-wavelength (λ~1.3 μm) InGaAsPNquantum-well lasers

We demonstrate high-performance InGaAsPN quantum well based long-wavelength lasers grown on GaAs substrates, nitrogen containing lasers emitting in the λ=1.2- to 1.3-μm wavelength range were grown by gas source molecular beam epitaxy using a RF plasma nitrogen source. Under pulsed excitation, lasers emitting at λ=1.295 μm exhibited a record low threshold current density (J_TH) of 2. 5 kA/cm². Lasers grown with less nitrogen in the quantum well exhibited significantly lower threshold current densities of J_TH =1.9 kA/cm² at λ=1.27 μm and J_TH=1.27 kA/cm² at λ=1.2 μm. We also report a slope efficiency of 0.4 W/A and an output power of 450 mW under pulsed operation for nitrogen containing lasers emitting at 1.2 μm     

Fabrication of Microcavity Light-Emitting Diodes Using Highly Reflective AlN–GaN and Ta2O 5–SiO2 Distributed Bragg Mirrors

We report the fabrication of microcavity light-emitting diodes (MCLEDs) with high reflectivity and crack-free AlN-GaN distributed Bragg reflector (DBR). The 5lambda microcavity structure consists of an n-type GaN, ten pairs InGaN-GaN multiple quantum wells and p-type GaN sandwiched between the hybrid cavity mode of an AlN-GaN and a Ta₂O₅-SiO₂ DBR. The AlN-GaN DBR has 29 periods with insertion of six AlN-GaN superlattice layers showing a crack-free surface morphology and a high peak reflectivity of 99.4% with a stopband of 21 nm. The output power of MCLED is about 11 W at an injection current of 7 mA. The electroluminescence has a polarization property with a degree of polarization of about 51%.     

InP-based cylindrical microcavity light-emitting diodes

We have investigated the properties of InP-based microcavity light-emitting diodes (λ=1.6 μm). Our objective was mainly to study the effects of lateral confinement of optical modes, which was achieved by the wet oxidation of double In_0.52Al_0.48 As layers. The smallest devices had a cavity radius of 0.5 μm, which becomes comparable to λ/n, where n is the effective refractive index of the photon emitting heterostructure. Two types of devices were tested: the first without any mirrors in the vertical direction, and the second with a combination of MgF/ZnSe DBR (top) and silver (bottom) to produce a low Q~35-45. The latter type of devices exhibited higher output power and narrower spectral linewidth; otherwise, the characteristics were very similar The output slope efficiency monotonically decreases with reduction of lateral cavity size up to ~2-μm in diameter and then is enhanced again for smaller cavity sizes. The slope efficiency of the smallest device (aperture diameter 1 μm) is almost equal to that measured for the largest devices. The maximum output power measured from the devices is 30 μW. The far-field pattern of devices with aperture radii ranging from 1.5 to 20 μm shows an angular width (FWHM) of 50°. On the other hand, devices with smaller aperture (radius ~0.5 μm) exhibit an angular width of 20°. The measured small-signal modulation bandwidth increases from ~0.45 GHz for the larger devices to 0.8 GHz for the smallest devices. Our results indicate that microcavity effects can be observed with only lateral photon confinement, making device fabrication requirements less stringent compared to surface-emitting lasers     

Resonant cavity enhanced photoluminescence of tensile strained Ge/SiGe quantum wells on silicon-on-insulator substrate

The tensile strained Ge/SiGe multiple quantum wells （MQWs） grown on a silicon-on-insulator （SOI） substrate were fabricated successfully by ultra-high chemical vapor deposition. Room temperature direct band photoluminescence from Ge quantum wells on SOI substrate is strongly modulated by Fabry-Perot cavity formed between the surface of Ge and the interface of buried SiO2. The photoluminescence peak intensity at 1.58 μm is enhanced by about 21 times compared with that from the Ge/SiGe quantum wells on Si substrate, and the full width at half maximum （FWHM） is significantly reduced. It is suggested that tensile strained Ge/SiGe multiple quantum wells are one of the promising materials for Si-based microcavity lijzht emitting devices.     

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     

Single-mode operation of mushroom structure surface emitting lasers

Mushroom structure vertical cavity surface emitting lasers with a 0.6-μm GaAs active layer sandwiched by two Al_0.6Ga_0.4 As-Al_0.08Ga_0.92As multilayers as top and bottom mirrors are discussed. The lasers exhibit a 15-mA pulses threshold current at 880 nm. Single longitudinal and single transverse mode operation was achieved on lasers with a 5-μm-diameter active region of current levels near 2×l_th. The light output above threshold current was linearly polarized with a polarization ratio of 25:1     

Calculated performances of 1.3-μm vertical-cavitysurface-emitting lasers on InGaAs ternary substrates

1.3-μm vertical-cavity surface-emitting lasers (VCSEL's) on InGaAs ternary substrates are proposed and designed, It is shown that a deep potential well on the ternary substrate enlarges optical gain of a strained quantum well in the wavelength region of 1.3 μm. A higher reflectivity distributed Bragg reflector (DBR) is also obtained by the use of the ternary substrate because materials with a large refractive-index difference can be used for the DBR. Calculated threshold current density of 1.3-μm VCSEL's on the ternary substrates is much lower than those on the conventional InP substrates. The possibility of extremely low threshold current density below 200 A/cm ² and temperature-insensitive operation are described     

1.57 μm strained-layer quantum-well GaInAlAs ridge-waveguidelaser diodes with high temperature (130°C) and ultrahigh-speed (17GHz) performance

The fabrication of GaInAlAs strained-layer (SL) multiple-quantum-well (MQW) ridge-waveguide (RW) laser diodes emitting at 1.57 μm is discussed. Due to an optimized layer structure, a very high characteristic temperature of 90 K was obtained. As a consequence for episide-up mounted devices, the maximum continuous wave (CW)-operation temperature is 130°C. At room temperature, a maximum output power of 47 mW was measured for 600-μm-long lasers with one high-reflection coated facet. The low series resistance of 4 Ω (2 Ω) for 200-μm-(400-μm)-long devices yields an ultrahigh 3-dB bandwidth of 17 GHz. These static and dynamic properties also result from a high internal quantum-efficiency of 0.83 and a high differential gain of 5.5×10^-15 cm²     

Intracavity 1.549-μm pumped 1.634-μm Er:YAG lasers at 300 K

A novel method of generating 1.634-μm laser action from Er:YAG crystals pumped intracavity by an Er:glass laser emitting at 1.549 μm is described. Operation of the Er:glass laser at 1.549 μm (red shifted from the standard 1.532 μm, but with comparable output) at 500 K was obtained using mirrors with tailored spectral reflectivities. Several Er:YAG crystals ranging in concentration from 0.3% to 2% and in length from 1 cm to 8 cm were lased in the intracavity pumping arrangement. All the Er:YAG crystals lased in the ⁴I_13/2 :Y1(6544 cm^-1)-⁴I_15/2:Z6(424 cm ^-1) 1.634-μm transition at 300 K     

An efficient low voltage, high frequency silicon CMOS lightemitting device and electro-optical interface

A silicon light emitting device was designed and realized utilizing a standard 2-μm industrial CMOS technology design and processing procedure. The device and its associated driving circuitry were integrated in a CMOS integrated circuit and can interface with a multimode optical fiber. The device delivers 8 nW of optical power (450-850 nm wavelength) per 20-μm diameter of chip area at 4.0 V and 5 mA. The device emits light by means of a surface assisted Zener breakdown process that occurs laterally between concentrically arranged highly doped n⁺ rings and a p⁺ centroid, which are all coplanarly arranged with an optically transparent Si-SiO₂ interface. Theoretical and experimental determinations with capacitances and series resistances indicate that the device has an intrinsic high-frequency operating capability into the near gigahertz range     

Monolithic photovoltaic PbS-on-Si infrared-sensor array

The growth of epitaxial narrow-gap PbS-on-Si substrates using a stacked CaF₂-BaF₂ intermediate buffer layer and the fabrication of linear arrays of photovoltaic infrared (IR) sensors in the PbS layer are discussed. The sensors of the array exhibit resistance-area products at zero bias of 3 Ω-cm² at 200 K (3.4-μm cutoff wavelength) and 2×10⁵ Ω-cm ² at 84 K (4-μm cutoff), with corresponding detectivities of 2×10¹⁰ and 1×10¹³ cm-√Hz/W, respectively     

Microwave performance of AlInAs-GaInAs HEMTs with 0.2- and0.1-μm gate length

The millimeter-wave performance is reported for Al_0.48In_0.52As-Ga_0.47In_0.53 As high-electron-mobility transistors (HEMTs) with 0.2-μm and 0.1-μm-long gates on material grown by molecular-beam epitaxy on semi-insulating InP substrates. Devices of 50-μm width exhibited extrinsic transconductances of 800 and 1080 mS/mm, respectively. External f_T (maximum frequency of oscillation) of 120 and 135 GHz, respectively, were measured. A maximum f_T of 170 GHz was obtained from a 0.1×200-μm² device. A minimum noise figure of 0.8 dB and associated gain of 8.7 dB were obtained from a single-stage amplifier at frequencies near 63 GHz     

New Ti-SALICIDE process using Sb and Ge preamorphization forsub-0.2 μm CMOS technology

A new process for thin titanium self-aligned silicide (Ti-SALICIDE) on narrow n⁺ poly-Si lines and n⁺ diffusion layers using preamorphization implantation (PAI) with heavy ions of antimony (Sb) and germanium (Ge) has been demonstrated for application to 0.2-μm CMOS devices and beyond. Preamorphization enhances the phase transformation from C₄₉Ti_xSi _x to C₅₄TiSi₂ and lowers the transformation temperature by 80°C so that it occurs before conglomeration in narrow lines. Preamorphization by Sb and Ge implantation yields better results than that by As. The sheet resistance of TiSi₂ on heavily As doped poly-Si lines are 3.7 Ω/□ and 3.8 Ω/□ for the samples preamorphized by Ge and Sb implantations even with line width down to 0.2 μm. There is less leakage in the Ti-SALICIDE diode with preamorphization than without it. The probable reasons and mechanisms are discussed     

⟨110⟩-oriented GaAs MESFETs

GaAs metal semiconductor field-effect transistors (MESFETs) have been successfully fabricated on molecular-beam epitaxial (MBE) films grown on the off-axis (110) GaAs substrate. The (110) substrates were tilted 6° toward the (111) Ga face in order to produce device quality two-dimensional MBE growth. Following the growth of a 0.4-μm undoped GaAs buffer, a 0.18-μm GaAs channel with a doping density of 3.4×10¹⁷ cm^-3 and a 0.12-μm contact layer with a doping density of 2×10¹⁸ cm^-3, both doped with Si, were grown. MESFET devices fabricated on this material show very low-gate leakage current, low output conductance, and an extrinsic transconductance of 200 mS/mm. A unity-current-gain cutoff frequency of 23 GHz and a maximum frequency of oscillation of 56 GHz have been achieved. These (110) GaAs MESFETs have demonstrated their potential for high-speed digital circuits as well as microwave power FET applications     

Characteristics of GaAsSb single-quantum-well-lasers emitting near1.3 μm

We report data on GaAsSb single-quantum-well lasers grown on GaAs substrates. Room temperature pulsed emission at 1.275 μm in a 1250-μm-long device has been observed. Minimum threshold current densities of 535 A/cm² were measured in 2000-μm-long lasers. We also measured internal losses of 2-5 cm^-1, internal quantum efficiencies of 30%-38% and characteristic temperatures T₀ of 67°C-77°C. From these parameters, a gain constant G₀ of 1660 cm^-1 and a transparency current density J_tr of 134 A/cm² were calculated. The results indicate the potential for fabricating 1.3-μm vertical-cavity surface-emitting lasers from these materials     

Hybrid dry-wet chemical etching process for via holes for galliumarsenide MMIC manufacturing

Through the wafer via-hole connections for monolithic microwave integrated circuits (MMIC) manufacturing have been developed by combining reactive ion etching (RIE) and wet chemical spray etching processes for 100-μm-thick gallium arsenide wafers. The dry process is based on the use of SiCl₄-BCl₃-Cl₂ and BCl₃-Cl₂ gas mixtures at room temperature is a reactive ion etcher. The etching parameters are optimized for anisotropic etching, initially, followed by slightly isotropic etching. To remove the residual `lip' and surface roughness, following reactive ion etching, a dynamic wet chemical spray etching based on H₃PO₄-H₂O₂-H₂O at 45°C is used. The combined dry-wet etching approach is used to fabricate <120-μm diameter via-holes in 100-μm-thick GaAs substrates with a wider process latitude. With this process, the authors have achieved >95 percent yield across 3-in wafers. Metallized via-hole contacts to power FET chips show a contact resistance <20 mΩ per via for 5-μ-thick selective gold plating     

Proton implanted VCSEL's for 3 Gb/s data links

Transverse single-mode and multimode intensity modulated butt-coupled InGaAs vertical cavity surface emitting lasers (VCSEL)s are investigated as a light source for optical fiber communication systems. Data transmission at 3 Gb/s with a bit error rate (BER) of less than 10 ^-11 is reported for both 4.3 km of standard fiber, as well as 0.5 km of multimode graded-index fiber, 10-μm active diameter single-mode VCSELs are shown to have lower mode competition noise requiring 3 dB and 6 dB less power at the front end receiver at a BER of 10^-11 compared to 19-μm and 50-μm active diameter devices, respectively. In data transmission with multimode VCSELs, the dispersion penalty is lower than for single-mode sources since the noise at the receiver is mainly determined by transmitter-mode competition noise     

Increase of parasitic resistance in shallow p+ extensionby SiN sidewall process and its improvement by Ge preamorphization forsub-0.25-μm pMOSFET's

Anomalously high parasitic resistance is observed when SiN gate sidewall spacer is incorporated into sub-0.25-μm pMOSFET's. The parasitic resistance in p⁺ S/D extension region increases remarkably by decreasing BF₂ ion implantation energy to lower than 10 keV. It is confirmed that low activation efficiency of boron in p⁺ extension is the reason for such high parasitic resistance. The reduction of activation efficiency of boron may result from hydrogen passivation of boron acceptor; Fourier transform infrared absorption (FT-IR) measurement suggests that diffused hydrogen from SIN into p⁺ extension region forms the silicon-hydrogen-boron complex. It is also found that the activation efficiency of boron correlates well both with implantation energy of BF₂ and the amorphization rate of substrate. Therefore, in sub-0.25-μm era, the extra amorphization step is essential not only to form a shallow junction but also to enhance boron activation. Germanium preamorphization implantation (Ge PAI) is hence applied to p⁺ extension of 0.15 μm pMOSFET's. It is finally demonstrated that this Ge PAI process reduces the total parasitic resistance to improve the drain saturation current by up to 10%