Recombination and loss mechanisms in low-threshold InAs-GaAs 1.3-/spl mu/m quantum-dot lasers

We show that even in quantum-dot (QD) lasers with very low threshold current densities (J/sub th/=40--50 A/cm/sup 2/ at 300 K), the temperature sensitivity of the threshold current arises from nonradiative recombination that comprises /spl sim/60% to 70% of J/sub th/ at 300 K, whereas the radiative part of J/sub th/ is almost temperature insensitive. The influence of the nonradiative recombination mechanism decreases with increasing hydrostatic pressure and increasing band gap, which leads to a decrease of the threshold current. We also studied, for the first time, the band gap dependence of the radiative part of J/sub th/, which in contrast increases strongly with increasing band gap. These results suggest that Auger recombination is an important intrinsic recombination mechanism for 1.3-/spl mu/m lasers, even in a very low threshold QD device, and that it is responsible for the temperature sensitivity of the threshold current.     

The temperature dependence of 1.3- and 1.5-μm compressivelystrained InGaAs(P) MQW semiconductor lasers

We have studied experimentally and theoretically the spontaneous emission from 1.3- and 1.5-μm compressively strained InGaAsP multiple-quantum-well lasers in the temperature range 90-400 K to determine the variation of carrier density n with current I up to threshold. We find that the current contributing to spontaneous emission at threshold I_Rad is always well behaved and has a characteristic temperature T₀ (I_Rad)≈T, as predicted by simple theory. This implies that the carrier density at threshold is also proportional to temperature. Below a breakpoint temperature T_B, we find I α n^Z, where Z=2. And the total current at threshold I_th also has a characteristic temperature T₀ (I_th)≈T, showing that the current is dominated by radiative transitions right up to threshold. Above T_B, Z increases steadily to Z≈3 and T₀ (I_th) decreases to a value less than T/3. This behavior is explained in terms of the onset of Auger recombination above T_B; a conclusion supported by measurements of the pressure dependence of I_th. From our results, we estimate that, at 300 K, Auger recombination accounts for 50% of I_th in the 1.3-μm laser and 80% of I_th in the 1.5-μm laser. Measurements of the spontaneous emission and differential efficiency indicate that a combination of increased optical losses and carrier overflow into the barrier and separate confinement heterostructure regions may further degrade T₀ (I_th) above room temperature     

A quantitative study of radiative, Auger, and defect related recombination processes in 1.3-/spl mu/m GaInNAs-based quantum-well lasers

By measuring the spontaneous emission (SE) from normally operating /spl sim/1.3-/spl mu/m GaInNAs-GaAs-based lasers we have quantitatively determined the variation of each of the current paths present in the devices as a function of temperature from 130 K to 370 K. From the SE measurements we determine how the current I close to threshold, varies as a function of carrier density n, which enables us to separate out the main current paths corresponding to monomolecular (defect-related), radiative or Auger recombination. We find that defect-related recombination forms /spl sim/55% of the threshold current at room temperature (RT). At RT, radiative recombination accounts for /spl sim/20% of I/sub th/ with the remaining /spl sim/25% being due to nonradiative Auger recombination. Theoretical calculations of the threshold carrier, density as a function of temperature were also performed, using a ten-band k /spl middot/ p Hamiltonian. Together with the experimentally determined defect-related, radiative, and Auger currents we deduce the temperature variation of the respective recombination coefficients (A, B, and C). These are compared with theoretical calculations of the coefficients and good agreement is obtained. Our results suggest that by eliminating the dominant defect-related current path, the threshold current density of these GaInNAs-GaAs-based devices would be approximately halved at RT. Such devices could then have threshold current densities comparable with the best InGaAsP/InP-based lasers with the added advantages provided by the GaAs system that are important for vertical integration.     

Investigation of 1.3-/spl mu/m GaInNAs vertical-cavity surface-emitting lasers (VCSELs) using temperature, high-pressure, and modeling techniques

We have investigated the temperature and pressure dependence of the threshold current (I/sub th/) of 1.3 /spl mu/m emitting GaInNAs vertical-cavity surface-emitting lasers (VCSELs) and the equivalent edge-emitting laser (EEL) devices employing the same active region. Our measurements show that the VCSEL devices have the peak of the gain spectrum on the high-energy side of the cavity mode energy and hence operate over a wide temperature range. They show particularly promising I/sub th/ temperature insensitivity in the 250-350 K range. We have then used a theoretical model based on a 10-band k.P Hamiltonian and experimentally determined recombination coefficients from EELs to calculate the pressure and temperature dependency of I/sub th/. The results show good agreement between the model and the experimental data, supporting both the validity of the model and the recombination rate parameters. We also show that for both device types, the super-exponential temperature dependency of I/sub th/ at 350 K and above is due largely to Auger recombination.     

A theoretical investigation of the characteristic temperature T/sub 0/ for semiconductor lasers

The temperature dependence of the characteristic temperature T/sub 0/ of semiconductor quantum-well lasers is investigated using detailed simulations. The critical-temperature-dependent processes are the optical gain and the nonradiative recombination. The gain model is based on k /spl middot/ p theory with the multiple quantum wells in the active layer represented by a superlattice. The Auger process is assumed to be thermally activated. It is shown that, with inclusion of the continuum state filling and interband mixing, the most important features experimentally observed in the temperature dependence of the T/sub 0/ value can be explained. The continuum state filling and band nonparabolicity cause a significant deviation from the ideal linear carrier density versus temperature relation for quantum wells. The results are compared to experiment for broad area devices lasing at 980 nm and 1.3, and 1.55 /spl mu/m, and show good agreement over a broad range of temperature.     

Carrier Dynamics in UV InGaN Multiple Quantum Well Inverted Hexagonal Pits

The emission and recombination characteristics of UV or blue light emission from InGaN/GaN quantum well (QW) structures influenced by V-shaped pits have been investigated by near-field and time-resolved photoluminescence measurements. Localization of charge carriers due to the potential barriers caused by the V-shaped pit formation is observed to be modified by thermal excitation. Temperature dependence of recombination dynamics shows evidence of a more complex potential barrier produced by the inverted hexagonal pits embedded within the multiple QWs. The emission from the narrow V-shaped pit QWs shows anomalous temperature dependence behavior that is significantly different from the emission from c-plane QWs. The carrier recombination process in c-plane QWs is significantly longer ~ 5 ns compared to the ~ 1.5 ns in V-shaped pit QWs at low temperatures due to the larger piezoelectric fields in wider wells. At room temperature, the recombination lifetimes are comparable due to increased carrier separation and delocalization within the V-shaped pit QWs.     

High-pressure studies of recombination mechanisms in 1.3-/spl mu/m GaInNAs quantum-well lasers

The pressure dependence of the components of the recombination current at threshold in 1.3-/spl mu/m GaInNAs single quantum-well lasers is presented using for the first time high-pressure spontaneous emission measurements up to 13 kbar. It is shown that, above 6 kbar, the rapid increase of the threshold current with increasing pressure is associated with the unusual increase of the Auger-related nonradiative recombination current, while the defect-related monomolecular nonradiative recombination current is almost constant. Theoretical calculations show that the increase of the Auger current can be attributed to a large increase in the threshold carrier density with pressure, which is mainly due to the increase in the electron effective mass arising from the enhanced level-anticrossing between the GaInNAs conduction band and the nitrogen level.     

The statistics of NBTI-induced V/sub T/ and /spl beta/ mismatch shifts in pMOSFETs

Negative bias temperature instability (NBTI) is a pFET degradation mechanism that can result in threshold voltage shifts up to 100 mV or more, even in very thin oxide devices. Since analog circuits that utilize matched pairs of devices, such as current mirrors and differential pairs, generally depend on V/sub T/ matching considerably better than this, NBTI-induced V/sub T/ mismatch shift may represent a serious reliability concern for CMOS analog applications. Furthermore, induced /spl beta/ mismatch shift (affecting drain current level at a fixed gate overdrive voltage) may also impact drain current and transconductance mismatch. In this paper, experimental results of the statistics and scaling properties of NBTI-induced V/sub T/ and /spl beta/ mismatch shifts in saturation, and models describing these results, are presented.     

ESD-induced oxide breakdown on self-protecting GG-nMOSFET in 0.1-/spl mu/m CMOS technology

Historically, the failure mode of the nMOS/lateral n-p-n (L/sub npn/) bipolar junction transistor (BJT) due to electrostatic discharge (ESD) is source-to-drain filamentation, as the temperature exceeds the melting temperature of silicon. However, as the gate-oxide thickness shrinks, the ESD failure changes over to oxide breakdown. In this paper, transmission line pulse (TLP) testing is combined with measurements of various leakage currents and numerical simulations of the electric field to examine the failure mode of an advanced 0.1-/spl mu/m CMOS technology, which is shown to be through gate-oxide breakdown. It is also shown by I/sub D/-V/sub G/ and I/sub G/-V/sub G/ measurements that the application of nondestructive ESD pulses causes gradual degradation of the oxide well before failure is reached, under the (leakage current) failure criteria used. Finally, the latent effects of stress-induced oxide degradation on the failure current I/sub f/ of the nMOS/L/sub npn/ are studied, and it is shown that as the device ages from an oxide perspective, its ESD protection capabilities decrease.     

A drain avalanche hot carrier lifetime model for n- and p-channel MOSFETs

A simple and physical drain avalanche hot carrier lifetime model has been proposed. The model is based on a mechanism of interface trap generation caused by recombination of hot electrons and hot holes. The lifetime is modeled as /spl tau/(I/sub d//W)/sup 2//spl prop/(I/sub sub//I/sub d/)/sup -m/. The formula is different from the conventional /spl tau/I/sub d//W-I/sub sub//I/sub d/ model in that the exponent of I/sub d//W is 2, which results from the assumed mechanism of the two-carrier recombination. It is shown that the mechanism gives a physical basis of the empirical /spl tau/-I/sub sub//W model for NMOSFETs. The proposed model has been validated experimentally both for NMOSFETs and for PMOSFETs. Model parameters extracted from experimental data show that carrier critical energies for creating damage are lower than the interface potential barriers. It is supposed that oxide band edge tailing enables low-energy carriers to create the damage. The channel hot electron condition becomes the worst case in short channel NMOSFETs, because gate voltage dependence of the maximum channel electric field decreases.     

Observations of NBTI-induced atomic-scale defects

A combination of MOSFET gate-controlled diode measurements and a very sensitive electron spin resonance technique called spin-dependent recombination was utilized to observe and identify defect centers generated by a negative bias temperature stress in fully processed SiO/sub 2/-based pMOSFETs. In SiO/sub 2/ devices, the defects include two Si/SiO/sub 2/ interface silicon dangling bond centers (P/sub b0/ and P/sub b1/) and may also include an oxide silicon dangling bond center (E'). The observations indicate that both P/sub b0/ and P/sub b1/ defects play major roles in these SiO/sub 2/-based devices and suggest that E' centers could play an important role.     

Performance and physics of quantum-dot lasers with self-assembledcolumnar-shaped and 1.3-μm emitting InGaAs quantum dots

This paper reports recent developments of our self-assembled InGaAs quantum-dot (QD) lasers and their unique physical properties. We achieved a low-threshold current of 5.4 mA at room temperature with our originally designed columnar-shaped QD's, and also, room-temperature 1.3-μm continuous-wave (CW) lasing with self-assembled dots grown at a decreased growth rate and covered by a strained InGaAs layer. We discuss influence of homogeneous broadening of single-dot optical gain on lasing spectra, influence of nonradiative carrier recombination on temperature characteristics of threshold currents, a model for the origin of the homogeneous broadening, a finding of random telegraph signals, and suppression of temperature sensitivity of interband emission energy by covering dots with a strained InGaAs layer     

Thermal-stability improvement of a sulfur-passivated InGaP/InGaAs/GaAs HFET

The temperature-dependent characteristics of an InGaP/InGaAs/GaAs heterostructure field-effect transistor (HFET), using the (NH/sub 4/)/sub 2/S/sub x/ solution to form the InGaP surface passivation, are studied and demonstrated. The sulfur-passivated device shows significantly improved dc and RF performances over a wide temperature range (300-510 K). With a 1/spl times/100-/spl mu/m/sup 2/ gate-dimension HFET by (NH/sub 4/)/sub 2/S/sub x/ treatment, the considerably improved thermal stability over dc performances including lower temperature variation coefficients on the turn-on voltage (-1.23 mV/K), the gate-drain breakdown voltage (-0.05 mV/K), the gate leakage current (1.04 /spl mu/A/mm/spl middot/K), the threshold voltage (-1.139 mV/K), and the drain-saturation-current operating regimes (-3.11/spl times/10/sup -4//K) are obtained as the temperature is increased from 300 to 510 K. In addition, for RF characteristics, the sulfur-passivated device also shows a low degradation rate on drain-saturation-current operating regimes (-3.29/spl times/10/sup -4//K) as the temperature is increased from 300 to 400 K. These advantages provide the promise for high-speed high-frequency high-temperature electronics applications.     

Investigation of multi‐layered‐gate electrode workfunction engineered recessed channel (MLGEWE‐RC) sub‐50 nm MOSFET: A novel design

In this paper, a two‐dimensional (2D) analytical sub‐threshold model for a novel sub‐50 nm multi‐layered‐gate electrode workfunction engineered recessed channel (MLGEWE‐RC) MOSFET is presented and investigated using ATLAS device simulator to counteract the large gate leakage current and increased standby power consumption that arise due to continued scaling of SiO₂‐based gate dielectrics. The model includes the evaluation of surface potential, electric field along the channel, threshold voltage, drain‐induced barrier lowering, sub‐threshold drain current and sub‐threshold swing. Results reveal that MLGEWE‐RC MOSFET design exhibits significant enhancement in terms of improved hot carrier effect immunity, carrier transport efficiency and reduced short channel effects proving its efficacy for high‐speed integration circuits and analog design. Copyright © 2008 John Wiley & Sons, Ltd.     

Experimental analysis of temperature dependence in 1.3-μmAlGaInAs-InP strained MQW lasers

We have analyzed experimentally the temperature and pressure dependences of the lasing characteristics of 1.3-μm AlGaInAs-InP strained multiple-quantum-well lasers, by focusing on the ratio of the nonradiative recombination current to the total current. The temperature dependence of the radiative current was studied by observing the spontaneous emission through a window in the substrate. It was found to increase linearly with temperature, exactly as expected for an ideal quantum well over the entire temperature range from 100 to 360 K. Further, it was shown that pure radiative recombination dominated the total current below a breakpoint temperature T_b of 220 K. Above this temperature, the onset of loss processes including Auger recombination caused a superlinear increase in the threshold current. Analysis of the linear and nonlinear components allowed us to determine the ratio of the nonradiative to radiative currents at threshold. We find that, relative to similar GaInAsP/InP lasers, there is a decrease in the nonradiative component of the current, resulting in a higher characteristic temperature T₀ in the AlGaInAs-InP lasers. At 300 K, the radiative recombination current is more than 70% of the total threshold current. This result is consistent with the observation that the threshold current increases by about 8% in 12-kbar hydrostatic pressure, while in GaInAsP lasers, a decrease of 10% or more is always observed over this pressure range     

Well-width dependent studies of InGaN-GaN single-quantum wellsusing time-resolved photoluminescence techniques

We present a well-width-dependent study of InGaN-GaN single-quantum wells using a time-resolved photoluminescence (PL) technique. At room temperature (RT), carrier recombination was found to be dominated by interface-related nonradiative processes. The dominant radiative recombination at RT was through band-to-band free carriers. For the sample grown at a higher growth rate, we observed a longer luminescence lifetime, which was attributed to an improved quantum-well (QW) interface. At low temperatures, the carrier recombination was found to be dominated by radiative recombination through a combination of free excitons, bound excitons, and free carriers. A decrease of radiative exciton lifetime was observed with decreased QW thickness     

Electron mobility in dense argon gas at several temperatures

The mobility /spl mu/ of excess electrons in dense Argon gas was measured as a function of the applied electric field E and of the gas density N at several temperatures in the range 142.6 < T < 200 K, encompassing the critical temperature T/sub c/ = 150.86 K We report here measurements up to N /spl ap/ 7 nm/sup -3/, close to the critical density, N/sub c/ /spl ap/ 8.1 nm/sup -3/. At all temperatures, and up to moderately high densities, the density-normalized mobility /spl mu/N shows the usual electric field dependence in a gas with a Ramsauer-Townsend minimum due to the mainly attractive electron-atom interaction. /spl mu/N is constant and field independent for small E, shows a maximum for a reduced field E/N /spl ap/ 4 mTd, and then decreases rapidly with the field. The zero field density-normalized mobility /spl mu//sub 0/N, for all T > T/sub c/, shows the well known anomalous positive density effect, i.e., /spl mu//sub 0/N increases with increasing N. Below T,, however, /spl mu//sub 0/N does not show the expected effect, but features a broad maximum. This appears to be a crossover behavior between the positive density effect shown for T > T, and the small negative effect previously observed for T /spl ap/ 90 K However, the data at all temperatures confirm the interpretation of the anomalous density effect as being essentially due by the density-dependent quantum shift of the electron ground state kinetic energy in a disordered medium as a result of multiple scattering (MS) processes, although other MS processes influence the experimental outcome.     

Impact of STI on the reliability of narrow-width pMOSFETs with advanced ALD N/O gate stack

For the first time, a shallow trench isolation (STI)-induced enhanced degradation in pMOSFETs for ultrathin gate oxide devices has been observed. The I/sub D/ degradation is enhanced as a reduction in the gate width and the hot carrier (HC) or negative bias temperature instability (NBTI) effect. Extensive studies have been compared for atomic layer deposition (ALD)-grown and plasma-treated oxide pMOSFETs. Different temperature dependences were observed. At room temperature, hole trap is dominant for the device degradation, in which hole-trap-induced V/sub T/ is significant, whereas at high temperature under NBTI stress, interface trap becomes more significant, which dominates the device I/sub D/ degradation. In addition, the V/sub T/ rolloff can be modeled as a width narrowing effect specifically for STI. More importantly, the NBTI-induced interface/oxide traps are strongly related to the hydrogen and N/sub 2/ content in the gate oxide formation process. The interface trap generation is suppressed efficiently using the ALD-grown gate oxide. These results provide a valuable guideline for the understanding of the HC and NBTI reliabilities in an advanced ALD-grown gate oxide processes/devices.     

Lasing at 1.28 /spl mu/m of InAs-GaAs quantum dots with AlGaAs cladding layer grown by metal-organic chemical vapor deposition

We report the device characteristics of stacked InAs-GaAs quantum dot (QD) lasers cladded by an Al/sub 0.4/Ga/sub 0.6/As layer grown at low temperature by metal-organic chemical vapor deposition. In the growth of quantum dot lasers, an emission wavelength shifts toward a shorter value due to the effect of postgrowth annealing on quantum dots. This blueshift can be suppressed when the annealing temperature is below 570/spl deg/C. We achieved 1.28-/spl mu/m continuous-wave lasing at room temperature of five layers stacked InAs-GaAs quantum dots embedded in an In/sub 0.13/Ga/sub 0.87/As strain-reducing layer whose p-cladding layer was grown at 560/spl deg/C. From the experiments and calculations of the gain spectra of fabricated quantum dot lasers, the observed lasing originates from the first excited state of stacked InAs quantum dots. We also discuss the device characteristics of fabricated quantum dot lasers at various growth temperatures of the p-cladding layer.     

InGaN-based blue laser diodes

The continuous-wave (CW) operation of InGaN multiquantum-well (MQW) structure laser diodes (LDs) was demonstrated at room temperature (RT) with a lifetime of 100 h. The threshold current and the voltage of the LDs were 50 mA and 5 V, respectively. The threshold current density was 8.8 kA/cm². The carrier lifetime and the threshold carrier density were estimated to be 3.5 ns and 1.8×10²⁰/cm³, respectively. The Stokes shift of the energy difference between the absorption and the emission energy of the InGaN MQW LD's were 140 meV. Both spontaneous and stimulated emission of the LD's originated from this deep localized energy state which is equivalent to a quantum dot-like state. From the measurements of gain spectra and an external differential quantum efficiency dependence on the cavity length, the differential gain coefficient, the transparent carrier density, threshold gain and internal loss were estimated to be 5.8×10^-17 cm², 9.3×10 ¹⁹ cm^-3, 5200 cm^-1, and 43 cm^-1 respectively