Stable transverse mode emission in vertical-cavity surface-emittinglasers antiguided by amorphous GaAs layer

The authors report the successful development of a method stabilising the fundamental transverse mode of a vertical-cavity surface-emitting laser using a low-temperature-deposited amorphous GaAs (a-GaAs) layer of a high refractive index. For a device of 10 μm diameter, stable fundamental mode emission has been observed over a wide range of current. Results are attributed to the antiguide effect of the a-GaAs-buried structure     

Transverse mode control of vertical-cavity top-surface-emittinglasers

Transverse mode characteristics and control for vertical-cavity top-surface-emitting lasers (VCSELs) are discussed. A spatial filtering concept for the control of VCSEL transverse modes that allows over 1.5-mW single TEM₀₀ transverse mode emission to be routinely achieved from continuous-wave electrically excited VCSELs is introduced. Without spatial filtering, L-I and V-I kinks are observed     

Polarization stabilization in vertical-cavity surface-emittinglasers through asymmetric current injection

We present experimental evidence that asymmetric current injection in intracavity contacted vertical-cavity surface-emitting lasers (VCSELs) stabilizes the polarization of the emitted light. Anisotropies in the gain and loss mechanisms introduced by asymmetric current injection are considered to explain this effect. The design scheme opens perspectives to obtain actual polarization control in VCSELs     

Transverse mode selection with a passive antiguide region invertical cavity surface emitting lasers

We report a numerical analysis on the transverse mode behavior of a novel passive antiguide region buried heterostructure vertical cavity surface emitting laser, which emits a single stable transverse mode from a large aperture. Two- and three-dimensional beam propagation methods were used to calculate the threshold gains and the actual modal profiles for the fundamental and first order modes. We show that the passive antiguide structure is the main modal selection mechanism and the high order modes suffer much higher losses such that they are highly suppressed from reaching thresholds     

Electrical polarization control of vertical-cavity surface-emittinglasers using polarized feedback and a liquid crystal

We report electrical control of the polarization state of a vertical-cavity surface-emitting laser (VCSEL), The VCSEL is subject to strong external optical feedback (up to 6% of emission), with polarization controlled by a liquid-crystal (LC) element, It is found that the contrast ratio of the complete system can be enhanced compared to the contrast ratio of the LC element alone     

Degradation behavior of 850-nm vertical-cavity surface-emittinglasers with an air-post index-guide structure

The degradation mechanism of a vertical-cavity surface-emitting laser (VCSEL) with an air-post structure is analyzed for stable optical parallel interconnection communication. It is clarified that the degradation is caused by the behavior of latent defects in the GaAs active layer. Decreasing the defects in the active region as well as decreasing the threshold current is important for obtaining a long-lifetime VCSEL     

Transverse mode control in InGaAsP/InP buried crescent diode lasers

Transverse mode stabilisation of InGaAsP/InP buried crescent laser diodes emitting at 1.3 ?m is described. Width and thickness of the active region have been reduced to stabilise the transverse mode. Operation up to 17 mW/facet in a stable transverse mode and threshold current as low as 12 mA in CW operation have been obtained.     

Improvement In AlGaAs/GaAs HBT power gains with buried proton-implanted layer

A new structure for AlGaAs/GaAs heterojunction bipolar transistors (HBTs) that employs a buried proton-implanted external collector layer is proposed. This structure has been successfully used to achieve high-performance HBTs with maximum oscillation frequencies fmax up to 51 GHz for a device with 2 ?×5 ?m emitter and 4 ?m×7 ?m collector dimensions.     

Lasing mode selection in vertical-cavity surface emitting-laserdiodes

A detailed model, including current spreading, carrier diffusion, and corresponding modal gains, is developed for a well-defined vertical-cavity surface-emitting laser structure. Above-threshold-operation (hole burning) is also analyzed by the model to quantitatively demonstrate the influence of injecting contact geometry and size in determining monomode operation. Results from this model demonstrate the importance of modal gain dynamics in establishing stable operation of such devices and hence the model may be used for improved device design     

Effects of buried layer geometry on characteristics of doublepolysilicon bipolar transistors

Dependences of electrical characteristics of double polysilicon transistors on n⁺ buried islands (subcollector) are examined. By simply modifying layouts of the buried island, the Early voltage (V _A), collector-to-emitter breakdown voltage (BV_CEO), and β×V_A product of transistors are increased from 42, 5.6, and 3070 V to 61, 6.7, and 3820 V, respectively, while the peak cutoff frequency at a V_CE of 1.5 V is decreased from around 21 to 17 GHz. Exploiting these results, it may be feasible to inexpensively integrate transistors with better f _T-BV_CEO and f_T-V_A tradeoffs for analog and power handling characteristics along with transistors optimized for high-speed operation. These results also indicate that the buried island geometry control could be an issue for controlling electrical characteristics for scaled bipolar transistors     

Reliability of amorphous InGaZnO TFTs with ITO local conducting buried layer for BEOL power transistors

The device reliability of a-IGZOTFTs with ITO local conducting buried layer (LCBL) has been investigated under positive gate bias stress and hot carrier stress for the application as BEOL power transistors. The drive current of a-IGZO TFTs could be controlled by the modulation of ITO LCBL thickness and distance under source/drain electrode. The threshold voltage shifts, the drain current degradation, and breakdown voltage have been measured and discussed according to the different ITO LCBL thickness and distance. The devices with thick ITO and short ITO distance are desirable for a power device for High/Low type I/O bridges. The devices with thin ITO and long ITO distance are desirable for Low/High type I/O bridges. The breakdown voltages are decreased with the increase of ITO thickness.     

Origin and modeling of the frequency dependent output conductancein microwave GaAs MESFET's with buried p layer

This paper presents the results of measurements and modeling of the frequency dependent output admittance of GaAs microwave MESFET's with and without the buried p layer constructions. The output conductance of devices without the buried p layer shows a transition from a low to a higher value typically within the frequency range of 10 Hz-100 Hz at 300 K, and 10 KHz-100 KHz at 367 K. The shape of this transition is determined by the presence of multiple deep levels at the channel-substrate interface, while the magnitude of the higher value of the output conductance is determined by the transconductance of the substrate-controlled parasitic FET. The addition of a buried p layer beneath the channel region results in a parasitic n-p-n bipolar transistor without completely eliminating the parasitic FET action. Results of our study show that the combined effects of these two parasitic transistors on the output conductance of the buried p layer device becomes relatively independent of frequency above 10 Hz at 300 K. However, at higher temperatures the frequency dispersion of the output conductance becomes significant at frequencies above 10 Hz. At low frequencies the parasitic FET causes a very high output capacitance, whereas the parasitic BJT action causes a high negative output capacitance. For the purpose of modeling of the output admittance, this paper indicates how the parameters of the parasitic FET and BJT can be determined by direct measurements on the MESFET's. The paper also suggests how the parameters of these parasitic transistors can be tailored by possible device structural changes, in order to achieve MESFET's with negligible dispersion of output conductance     

Monolithic integration of a GaAs MESFET with a resonant cavity LED using a buried oxide layer

A new method to monolithically integrate a GaAs MESFET and a resonant cavity InGaAs QW LED is demonstrated. Current confinement in these two dissimilar devices is accomplished using a buried insulating layer formed by the thermal oxidation of AlAs. Fabrication and device performance under dc bias as well as modulation results are briefly described.     

Negative bias illumination stress instability in amorphous InGaZnO thin film transistors with ITO local conducting buried layer

The investigations on the device instabilities of amorphous InGaZnO thin film transistors (a-IGZO TFTs) with ITO local conducting buried layer (LCBL) under the source/drain region and in the middle of the active channel region have been performed under negative bias and illumination stress. From the increased drain current of a-IGZO with ITO LCBL, one can control the drive current by modulating the length of ITO LCBL without changing the ratio of channel width and length. The reason for the less degradation of a-IGZO TFTs with LCBL under negative bias stress than that of device without LCBL was explained by the fact that ITO LCBL could act to reduce the effective energy barrier and act as a hole damping layer. However, the device degradation of a-IGZO with ITO LCBL under negative bias and illumination stress was more significant than that of one without LCBL due to the electron hole pair generation in ITO layer under illumination.     

W-band monolithic frequency doubler using vertical GaAs varactor diode with n/sup +/ buried layer

A W-band monolithic frequency doubler was designed and fabricated using a vertical GaAs varactor diode that has an n/sup +/ buried layer and uses a mesa isolation process. An output power of 30 mW was obtained from this chip at 93 GHz with a conversation efficiency of 12%. This is believed to be the first reported W-band monolithic varactor diode frequency doubler.<>     

Single-transverse mode and stable-polarization operation underhigh-speed modulation of InGaAs-GaAs vertical-cavity surface-emittinglaser grown on GaAs (311) B substrate

We have demonstrated an oxide confinement vertical-cavity surface-emitting laser grown on a GaAs (311)B substrate, and achieved single-transverse mode and single-polarization operation in the entire tested current range. The threshold was 0.6 mA for a 2.7 μm×2.9 μm oxide aperture. Even under high-speed modulation up to 5 GHz, the device showed stable single-transverse mode and polarization. Sidemode suppression ratio and orthogonal polarization suppression ratio were over 30 and 10 dB, respectively     

High temperature characteristics of GaAs MESFET devices fabricatedwith AlAs buffer layer

We have investigated the influence of AlAs buffer layers on MESFET drain leakage current at temperatures from 25-350°C. The experimental results show that subthreshold drain leakage current is substantially decreased with increasing AlAs layer thickness. For a 1 μm×200 μm MESFET with 2500 Å of AlAs buffer layer, we have obtained 78 μA of subthreshold drain leakage current at 350°C ambient temperature. This leakage current value is a factor of 2.5 improvement over the best previously reported results at 350°C     

Effects of the undoped layer on characteristics of amorphous silicon Schottky diodes

The effects of undoped layer thickness on the dark and illuminated I-V characteristics of hydrogenated amorphous silicon Schottky barrier solar cells are investigated. Schottky barrier (S.B.) metals having different work function (Cr and Pd) were deposited on the 0.22 µm - 1.45 µm thick a-Si:H films. Photovoltaic performance, Jsc, Voc, FF and efficiency, are independent of thickness of the undoped layer if film thickness is larger than the depletion region width. Jscand Vocare controlled by S.B. metal and FF is independent of S.B. metal. Dark I-V characteristics depend on both S.B. metal and device thickness suggesting a barrier controlled space charge limited phenomena. Variation of turn-on (threshold) voltage with undoped layer thickness can be applied to the design of switching and memory devices.     

Fabrication and characteristics of a GaInP/GaAs heterojunctionbipolar transistor using a selective buried sub-collector

A C-doped GaInP/GaAs heterojunction bipolar transistor (HBT) with a selective buried sub-collector has been fabricated by two growth steps. The active HBT region was made on the selective buried sub-collector layer with minimum overlap of the extrinsic base and the sub-collector region resulting in substantial reduction of the base-collector capacitance. The experiment shows that the base-collector capacitance is reduced to about half of that of a conventional HBT while the base resistance remains unchanged resulting in a 40-50% increase in the maximum oscillation frequency. Both DC and RF characteristics are investigated and compared with a conventional HBT. A current gain of 40, cutoff frequency of 50 GHz and maximum oscillation frequency of 140 GHz were obtained for the GaInP/GaAs HBT. It is demonstrated that the selective buried sub-collector provides an effective means for enhancing RF performance of an HBT