Electrically-pumped vertical-cavity lasers with Al/sub x/O/sub y/-GaAs reflectors

We have fabricated the first electrically-pumped vertical-cavity surface-emitting lasers (VCSELs) which use oxide-based distributed Bragg reflectors (DBRs) on both sides of the gain region. They require a third the epitaxial growth time of VCSELs with semiconductor DBRs. We obtain threshold currents as low as 160 /spl mu/A in VCSELs with an active area of 8 /spl mu/m/spl times/8 /spl mu/m using a two quantum well InGaAs-GaAs active region. By etching away mirror pairs from the top reflector, quantum efficiencies as high as 61% are attained, while still maintaining a low threshold current of 290 /spl mu/A.     

Sub-mA threshold 1.5-/spl mu/m VCSELs with epitaxial and dielectric DBR mirrors

In this letter, we report low threshold 1.5-/spl mu/m vertical-cavity surface-emitting lasers with epitaxial and dielectric distributed Bragg reflector (DBRs). The device consists of a lattice-matched InAlAs-InAlGaAs DBR grown on an InP substrate, an InAlGaAs quantum well active region, a metamorphic GaAs tunnel junction, and a SiO/sub 2/-TiO/sub 2/ dielectric DBR. The current confinement is achieved by oxidizing an AlAs metamorphic layer grown on top of the active region. Small aperture devices show a minimum threshold of 0.8 mA at room temperature in continuous-wave operation.     

Transient negative photocurrent and out-of-well dipole kinetics in novel piezoelectric InGaAs/GaAs MQW pin diodes

In 111B InGaAs/GaAs pin structures with a multiple quantum well (MQW) embedded region, the average internal field in the active MQW region can be tailored to obtain device configurations with a negative average field (NAF), opposite to the built-in field. In 111 NAF diodes, carriers photogenerated at the wells become trapped early at the potential minima located at the ends of the active region thus creating an electric dipole. In this work, in 111 NAF devices with a 0.17 In mole fraction layers, by using time-resolved photocurrent and a novel optical-pump electrical-probe techniques, we report the presence of a negative transient photocurrent, a direct quantitative evidence of such dipole formation, and we present measurements of its extinction kinetics at room temperature.     

High-power room temperature emission quantum cascade lasers at /spl lambda/=9 /spl mu/m

We present two different techniques for processing InP-based /spl lambda/=9 /spl mu/m quantum cascade lasers which improve the thermal dissipation in the device. The first process is based on hydrogen implantation creating an insulating layer to inject current selectively in one part of the active region. The second process uses a thick electroplated gold layer on the laser ridge to efficiently remove the heat produced in the active region. Each process is designed to improve heat evacuation leading to higher performances of the lasers and will be compared to a standard ridge structure from the same wafer. We give evidence that the process of proton implantation, efficient in GaAs based structures, is not directly applicable to InP based devices and we present a detailed analysis of the thermal properties of devices with an electroplated gold thick layer. With these lasers, an average power of 174 mW at a duty cycle of 40% has been measured at 10/spl deg/C.     

Interference effects in the electroreflectance and electroluminescence spectra of InGaN/AlGaN/GaN light-emitting-diode heterostructures

Interference effects in InGaN/AlGaN/GaN light-emitting-diode heterostructures of blue emission are studied by spectroscopy of electroreflectance and electroluminescence. The periodic bands observed in the electroreflectance and electroluminescence spectra in a blue spectral range are caused by interference effects in the structure in general. The emergence of interference fringes in the electroreflection spectra is explained by modulation of built-in electric fields in the active region of the heterostructure. The long-period interference fringes observed in the electroreflectance spectra in a wide spectral range from infrared to ultra-violet allows one to determine the location of the active region of the heterostructure with respect to different reflecting surfaces in the cavity.     

Effect of the active region thickness on characteristics of semiconductor lasers based on asymmetric AlGaAs/GaAs/InGaAs heterostructures with broadened waveguide

The effect of the active region thickness on the basic characteristics of high-power semiconductor lasers based on AlGaAs/GaAs/InGaAs asymmetric separate-confinement heterostructures grown by MOCVD epitaxy has been studied. It is shown that the threshold current, temperature sensitivity of the threshold current density, internal quantum efficiency of stimulated emission, and differential quantum efficiency are improved as the active region thickness increases. It is demonstrated that the maximum attainable optical emission power of a semiconductor laser and the internal quantum efficiency of photoluminescence are the most sensitive to defect formation in the heterostructure and become lower as the critical thickness of the strained In_xGa_1–x As layer in the active region is exceeded.     

Continuous-wave operation of 1.55-/spl mu/m vertical-cavity surface-emitting laser with digital-alloy active region using submonolayer superlattices

For the first time, a digital-alloy active region (DAAR) consisting of submonolayer superlattices was used in a 1.55-/spl mu/m vertical-cavity surface-emitting laser. The device showed continuous-wave operation with a room-temperature threshold current (I/sub th/) of 1.2 mA, maximum output power (P/sub max/) of 0.26 mW, and a differential quantum efficiency (/spl eta//sub d/) of 21%. These results indicate that the DAAR is at least as efficient as the analog-alloy active region and provides much better control of alloy composition and strain.     

Radiance saturation in small-area GaInAsP/InP and GaAlAs/GaAs LED's

The radiance/current relationship for small-area surface emitting LED's has been found to saturate at high current densities between 30 and 1000 kA/cm²in the various GaAlAs and GaInAsP devices investigated. An important saturation mechanism is found to be due to superluminescence in the plane of the active layer. Auger recombination and carrier leakage from the active region are generally of secondary importance in causing the saturation.     

Characteristics of p- and n-channelpoly-Si/Si1-xGex/Si sandwiched conductivitymodulated thin-film transistors

Both p- and n-channel poly-Si/Si_1-xGe_x/Si sandwiched conductivity modulated thin-film transistors (CMTFTs) are demonstrated and experimentally characterized. The transistors use a poly-Si/Si_1-xGe_x/Si sandwiched structure as the active layer to avoid the poor interface between the gate oxide and the poly-Si_1-xGe_x material. Also an offset region placed between the channel and the drain is used to reduce the leakage current. Furthermore, the concept of conductivity modulation in the offset region is used to provide a high on-state current. Results show that the transistors provide a high on-state current as well as a low leakage current compared to those of conventional offset drain TFTs. The p- and n-channel CMTFTs can be combined to form CMOS drivers, which are very suitable for use in low temperature large area electronic systems on glass applications     

1.3-μ m InGaAlAs Short-Cavity DBR Lasers for Uncooled 10-Gb/s Operation With Low Drive Current

We present a novel 1.3-mum laser, a short-cavity distributed-Bragg-reflector (DBR) laser that enables uncooled, 10-Gb/s operation with low drive currents. The laser consists of a short InGaAlAs multiple-quantum-well active region butt-jointed to an InGaAsP-DBR region. A fabricated laser with a 75-mum active region demonstrated 100 degC, 10-Gb/s operation at a record low drive current of 14-mA peak-to-peak (mA_p-p) with an average output power of -3 dBm     

Lasing in Cd(Zn)Se/ZnMgSSe heterostructures pumped by nitrogen and InGaN/GaN lasers

Photoluminescence and lasing at a wavelength of λ=510–530 nm (green spectral region) in Cd(Zn)Se/ZnMgSSe structures with a different design of the active region are studied in a wide range of temperatures and nitrogen laser pump intensities. A minimal lasing threshold of 10 kW/cm², a maximal external quantum efficiency of 12%, and a maximal output power of 20 W were obtained for the structure with the active region composed of three ZnSe quantum wells with fractional-monolayer CdSe inserts. The lasers exhibited a high temperature stability of the lasing threshold (characteristic temperature T ₀=330 K up to 100°C). For the first time, an integrated converter composed of a green Cd(Zn)Se/ZnMgSSe laser optically pumped by a blue InGaN/GaN laser that is grown on a Si (111) substrate and incorporates multiple quantum wells is suggested and studied.     

Proposal of a GaInAs/GaInAsP/InP antiguided filter laser arrayoperating in single longitudinal mode

The authors propose a type of in-phase lateral- and single-longitudinal-mode laser array, the so-called antiguided filter laser array (AFLA), in which an antiguided filter region is inserted between a positive-index-guided multiple-strip array region with a shallow corrugation grating and a high-reflectivity region with deep corrugation. Threshold current as low as 100 mA was obtained for a five-element laser array with active region length of 300 μm and total emitter width of 18 μm, using five-pairs of Ga_0.3In _0.7As (3 nm)/GaInAsP (10 nm) compressively strained quantum wells     

Study of tunneling transport of carriers in structures with an InGaN/GaN active region

Properties of light-emitting structures with an InGaN/GaN active region emitting in a range of 500–550 nm are studied. Photoluminescence of the structures is studied at various values of external bias and temperature as well as with time resolution. With the reverse bias, a decrease in the carrier lifetime associated with tunneling exit of the carriers from the active region is found. The mechanism of tunneling leakage is simulated allowing for the Boltzmann distribution of carriers by energy; it is shown that the calculated and experimental dependences agree well. It is shown that the tunneling transport exerts a considerable effect on the characteristics of structures with an InGaN/GaN active region.     

980-nm aluminum-free InGaAs/InGaAsP/InGaP GRIN-SCH SL-QW lasers

The design of 980-nm InGaAs/InGaAsP/InGaP GRIN-SCH lasers with aluminium-free GaAs-based materials is discussed. The first approach was successful MOCVD growth of InGaAsP alloy lattice matched to GaAs. It was found that an immiscible region existed, as determined by photoluminescence measurements. The main approach was to introduce the graded bandgap structure consisting of InGaAsP layers lattice matched to GaAs into GaAs/InGaP interfaces. The graded structure suppresses the heterojunction spikes, especially of the valence band at these interfaces. As a result, series resistance of GRIN-SCH lasers with the graded bandgap structure was reduced compared with simple SCH lasers with abrupt bandgap interfaces due to improved hole injection. Furthermore, the optimum graded structures for optical confinement region were investigated to improve the carrier injection efficiency, especially electron injection efficiency into a single quantum well active layer. Also, this graded bandgap structure formed the graded refractive index profile in an active region, which is the so-called GRIN-SCH waveguide. The GRIN-SCH profile could be controlled to narrow the transverse beam divergence for high coupling efficiency into a single-mode fiber and to reduce the optical power density at facets for high reliability. Finally the results of a life-test of GRIN-SCH lasers was shown, and the lifetime of GRIN-SCH lasers with immiscible InGaAsP layers was discussed     

Analysis of electrical, threshold, and temperature characteristics of InGaAsP/InP double- heterojunction lasers

This paper presents an extensive study of the fundamental characteristics of InGaAsP/InP double-heterojunction (DH) lasers with a wavelength of 1.3 μm. The confinement properties of injected carriers in the quaternary active region, the electrical properties such as leakage current and diode current versus voltage, the threshold characteristics, and the threshold temperature characteristics are determined through an analysis of the heterojunction energy band structure. The threshold temperature characteristics and the carrier leakage from the active region into the confining layers are examined in detail. To clarify the dependence of carrier leakage on lasing wavelength in InGaAsP/InP DH lasers and to explain the difference between GaAlAs/GaAs DH and InGaAsP/InP DH lasers, the barrier heights required to effectively confine the injected carriers and the effective carrier masses in the active region are discussed. Various possible explanations for the observed threshold temperature characteristics are considered.     

2.36 /spl mu/m diode pumped VCSEL operating at room temperature in continuous wave with circular TEM/sub 00/ output beam

Operation of a diode-pumped AlGaAsSb/GaInAsSb type-I quantum-well vertical cavity surface emitting laser emitting near 2.36 /spl mu/m is reported. The epitaxial structure, grown on GaSb by molecular beam epitaxy consists of a GaSb/AlAsSb Bragg reflector and a GaInAsSb/AlGaAsSb active region. A circular TEM/sub 00/ low-divergence laser operation is demonstrated in continuous-wave mode operation from 268 up to 308K. A threshold of 5.5 kW/cm/sup 2/ at 268K has been measured.     

A p-channel poly-Si/Si1-xGex/Si sandwichedconductivity modulated thin-film transistor

A p-channel poly-Si/Si_1-xGe_x/Si sandwiched conductivity modulated thin-film transistor (CMTFT) is proposed and demonstrated in this paper for the first time. This structure uses a poly-Si/Si_1-xGe_x/Si sandwiched structure as the active layer to avoid the poor interface between the gate oxide and the poly-Si_1-xGe_x material. Also an offset region placed between the channel and the drain is used to reduce the leakage current. Furthermore, the concept of conductivity modulation in the offset region is used to provide high on-state current. Results show that this structure provides high on-state current as well as low leakage current as compared to that of conventional offset drain TFTs. The on-state current of the structure is 1.3-3 orders of magnitude higher than that of a conventional offset drain TFT at a gate voltage of -24 V and drain voltage ranging from -15 to -5 V while maintaining comparable leakage current     

Compact, High-$Q$, and Low-Current Dissipation CMOS Differential Active Inductor

This letter presents an improved, compact, and tunable high-Q differential active inductor implemented in Silterra's industry standard 0.18 mum CMOS process. The improved differential active inductor demonstrates a Q ap 1000 at high frequency region. Low-current dissipation is achieved by reusing the current from the differential gyrator for stabilizer and negative impedance circuit. A replica bias circuit has been introduced to allow current-controlled inductance of the improved differential active inductor. Sensitivity of the improved differential active inductor to process variation is also included in this letter.     

InternalQswitching in GaAs- GaxAl1-xAs heterostructure lasers

Efficient internalQswitching and delay effects are observed in a range of temperatures from less than 100 to 400°K in solution grown GaAs-GaxAl1-xAs heterostructure injection laser diodes. The characteristic transition temperature Ttabove which long stimulated emission delays are found, decreases with the laser cavity length (i. e., higher threshold current density). Ttalso decreases with the thickness of the active region. The onset of hole injection seems to occur simultaneously with the appearance of the pronounced delay andQ-switching effects.     

Single wavelength grating filter laser array withGa0.3In0.7As/GaInAsP/InP strained MQW structure

Stable in-phase lateral- and single-longitudinal-mode operation up to four times the threshold (P_o~100 mW) was achieved in a five-element 1.5-μm-wavelength Ga_0.3In_0.7As/GaInAsP/InP compressive strained MQW grating filter laser array. The threshold current and external differential quantum efficiency under pulsed condition were 330 mA (emitter width of 18 μm, active region length of 480 μm) and 17%, respectively