Current Blocking Region Research Articles

High-Reliability Uncooled InGaAlAs Lasers with Unpumped Current Blocking Regions Near Cavity Facets

The facet heating of high-power laser diodes significantly influences device reliability. To mitigate facet temperature, current blocking (CB) regions are employed at both cavity facets of the laser. In this paper, we investigate the device characteristics of uncooled InGaAlAs lasers with CB facets. We observe two types of light versus current (LI) curves and propose corresponding physical models. Our findings demonstrate the high reliability performance of uncooled lasers with proper engineering design and CB process.

Performance Improvement of InGaN-Based LEDs via a Current-Blocking Region Prepared via Hydrogen Passivation

We report p-GaN passivation via hydrogen plasma used to create current blocking regions (CBRs) in InGaN-based green LEDs with standard dimensions of 280 × 650 μm2. The CBRs are created before mesa etching in two variants: underneath the opaque metal p-pad and both underneath the p-pad and along the device’s mesa perimeter. The peak EQE increased by 13% and 23% in the first and the second cases, respectively, in comparison to the reference LED with no CBR. With a high injection current of 50 A/cm2, the EQE value increased by 2% in the case of CBRs underneath the p-pad as well as by 14% in the case of CBRs both underneath the p-pad and along the mesa perimeter (relative to the reference sample with no CBR).

The Thermal Characteristics of AlGaN/GaN Hemts with Different Channel Width

In this study, the thermal characteristics of AlGaN/GaN HEMTs with different channel widths were investigated. The thermal characteristics including threshold voltage, maximum transconductance (gm,max), on-state current, and on-resistance were investigated from 30 to 150 °C with the increment of 10°C. All devices have the same source, gate and drain widths, but difference in the channel widths. The channel width (Wchannel) is determined by a current blocking region between the source and drain. Device A is a conventional device with gate width (WG) of 50 mm without the current blocking region. Therefore, the channel width is the same as the gate width. Device B, C, and D have the gate width of 50 mm but different channel widths of 27.5, 25, and 12.5 mm, respectively. The dimension of the channel width was implemented by ion-implantation at the process step of device isolation. All epitaxial layers were grown on Si substrate. All devices were passivated by a 200-nm PECVD SiN without field plates. The devices under test are with a gate-source distance (LGS) of 4-µm, a gate length (LG) of 2-µm, gate width (WG) of 50-µm, and a gate-drain distance (LGD) of 10-µm. At room temperature, device B, C, and D with smaller channel widths show the improved on-state current density, subthreshold swing, and gm. Device D shows a gm,max of 239 mS/mm compared to the 127 mS/mm of the device A. A significant improvement was observed in gm,max of device D due to the large ratio of WG/Wchannel. A better capability of the gate control is achieved. However, the thermal characteristics show the opposite trend. The measured thermal coefficients of the threshold voltage, gm,max, on-state current, and on-resistance of the device D are 2.1´10-4, -6.7´10-3, -3.4´10-3, and 1.1´10-2 1/°C compared with 1.5´10-5, -1.4´10-3, -2.1´10-3, and 7.2´10-3 1/°C of the device A. The possible reason is due to the current crowding at the corners of the blocking region. A suitable heatsink design or back side via are required to reduce the thermal impact. Figure 1

Direct Current Characteristics of AlGaN/GaN High-Electron-Mobility Transistors with Different Channel Widths

AlGaN/GaN high-electron-mobility transistors with different channel configurations were fabricated and characterized. Channel configuration was designed to have the source, gate, and drain metal contacts of the same size but with different channel widths, which was achieved by the current blocking region. Current density, subthreshold swing, and transconductance (gm) improved with the decreasing channel width. A significant improvement was observed in gm because of a large gate width (WG) to channel width (Wchannel) ratio. A device with a WG/Wchannel of 4 has a gm of 239 mS/mm, whereas a device with a WG/Wchannel of 1 has a gm of 127 mS/mm.

Improved Output Power of GaN-Based Vertical Light Emitting Diodes Fabricated with Current Blocking Region Formed by O2 Plasma Treatment

We report on the formation of current blocking regions by O2 plasma treatment to reduce current crowding at the active region above the p-type electrodes of GaN-based vertical light emitting diodes (LEDs). The forward voltage and reverse current (at -5 V) of the plasma-treated LEDs slightly increase with increasing aging time. The output power (at 350 mA) of the plasma-treated LEDs is enhanced by 26% as compared to that of reference LEDs and is comparable to that of LEDs with SiO2 current blocking layers. It is shown that the output power (at 700 mA) of the plasma-treated LEDs is degraded by less than 2% of the initial value after 500 h.

Improved Output Power of GaN-Based Vertical Light Emitting Diodes Fabricated with Current Blocking Region Formed by O2Plasma Treatment

Improved Output Power of GaN-Based Vertical Light Emitting Diodes Fabricated with Current Blocking Region Formed by O₂Plasma Treatment

Effect of oxygen plasma-induced current blocking on the performance of GaN-based vertical light-emitting diodes

We investigated the effect of O2 plasma-induced current blocking regions (O2-CBRs) on the performance of GaN-based vertical light-emitting diodes (VLEDs) as a function of the O2 plasma rf power. The VLEDs fabricated with the O2-CBRs give forward voltages in the range 3.41–3.48 V at 350 mA, which are slightly higher than those in the case of VLEDs with and without SiO2 current-blocking layers (CBLs). The output powers of VLEDs with O2-CBRs for rf powers of 50 and 100 W are 400.2 and 399.4 mW, respectively, which are slightly higher than those of the VLEDs with SiO2 CBLs. Indium tin oxide (ITO)-based contacts to p-GaN show rectifying behaviors with Schottky barrier heights of 1.89 and 2.78 eV, when treated at rf powers of 50 and 100 W, respectively. X-ray photoemission spectroscopy (XPS) results show that for the samples treated at 50 W, the Ga 2p core level moves toward the higher binding-energy side as compared to that of the reference sample without plasma treatment. On the basis of the electrical characteristics and XPS results, we state that the O2-CBR effect is due to the generation of donor-like defects at the p-GaN surface.

Enhanced characteristics of blue InGaN∕GaN light-emitting diodes by using selective activation to modulate the lateral current spreading length

We have studied the characteristics of blue InGaN∕GaN multiquantum-well light-emitting diodes (LEDs) after reducing the length of the lateral current path through the transparent layer through formation of a peripheral high-resistance current-blocking region in the Mg-doped GaN layer. To study the mechanism of selective activation in the Mg-doped GaN layer, we deposited titanium (Ti), gold (Au), Ti∕Au, silver, and copper individually onto the Mg-doped GaN layer and investigated their effects on the hole concentration in the p-GaN layer. The Mg-doped GaN layer capped with Ti effectively depressed the hole concentration in the p-GaN layer by over one order of magnitude relative to that of the as-grown layer. This may suggest that high resistive regions are formed by diffusion of Ti and depth of high resistive region from the p-GaN surface depends on the capped Ti film thickness. Selective activation of the Mg-doped GaN layer could be used to modulate the length of the lateral current path. Furthermore, the external quantum efficiency of the LEDs was improved significantly after reducing the lateral current spreading length. In our best result, the external quantum efficiency was 52.3% higher (at 100mA) than that of the as-grown blue LEDs.

Improving the Luminescence of InGaN–GaN Blue LEDs Through Selective Ring-Region Activation of the Mg-Doped GaN Layer

In this study, we used the selective ring-region activation technique to restrain the surface leakage current and to monitor the luminescence characteristics of InGaN-GaN multiple quantum-well blue light-emitting diodes (LEDs). To access the current blocking region after forming a periphery high-resistance ring-region of the Mg-doped GaN layer and to reduce the degree of carrier trapping by the surface recombination centers, we deposited a titanium film onto the Mg-doped GaN epitaxial layer to form a high-resistance current blocking region. To characterize their luminescence performance, we prepared LEDs incorporating titanium films of various widths of the highly resistive current blocking layer. The hole concentration in the Mg-doped GaN epitaxial layer decreased from 3.45times1017 cm-3 to 3.31times1016cm-3 after capping with a 250-nm-thick layer of titanium and annealing at 700 degC under a nitrogen atmosphere for 30 min. Furthermore, the luminescence characteristics could be improved by varying the width of the highly resistive region of the current blocking area; in our best result, the relative electroluminescence intensity was 30% (20 mA) and 50% (100 mA) higher than that of the as-grown blue LEDs

Facet temperature reduction by a current blocking layer at the front facets of high-power InGaAs/AlGaAs lasers

The facet heating of a single-quantum well InGaAs/AlGaAs broad-area high-power laser-diodes emitting at 940 nm was reduced by the introduction of a 30 μm long current blocking region located at the front facet of the laser, also increasing the level of catastrophical optical mirror damage. The blocking of the pump current close to the facet reduces the carrier density and then the surface recombination current. The temperature rise of 2 mm long and 200 μm wide lasers is reduced by a factor of 3–4.

2 W reliable operation in 50 µm-wide InGaAsP/InGaP/AlGaAs(λ = 810 nm) SQW diode lasers with tensile-strained InGaP barriers

A new InGaAsP/InGaP/AlGaAs (/spl lambda/=810 nm) laser with tensile-strained InGaP barriers, broad waveguide structure and current blocking region near the facet is reported. 2W continuous wave operation over 2000 h from a 50 /spl mu/m aperture was achieved.

All MOCVD grown 850-nm-wavelength refractive-index-guided semiconductor-buried vertical-cavity surface-emitting lasers with p/n-InGaP current blocking layers

All metal-organic chemical vapor deposition (MOCVD) grown 850-nm-wavelength refractive-index-guided semiconductor-buried vertical-cavity surface-emitting laser is proposed and their performance is investigated. P/n-InGaP current-blocking region enables both selective regrowth and the formation of refractive-index-guided region which surrounds multiquantum-well active/core regions. We have achieved room temperature CW operation of the new types of vertical-cavity surface-emitting lasers. The minimum threshold current was 9.5 mA with 18 /spl mu/m square mesa size at 30/spl deg/C. The device lased at up to 70/spl deg/C, and the maximum output power exceeds 1 mW at above 30/spl deg/C. The near field pattern indicates the single-lobed output beam at low bias current.

Design and realization of a buried-heterostructure tunable-twin-guide laser diode with electrical blocking regions

An InGaAsP-InP buried-heterostructure tunable-twin-guide (TTG) laser diode is presented, incorporating epitaxially regrown p-n-p-n current blocking regions to minimize current leakage around the active region in the ridge. The laser design is based on a theoretical model describing the mechanism of current leakage and the influence of electrical blocking regions by a two-dimensional computer simulation. The technological realization of the laser device reveals a way to achieve a self-aligned transverse blocking region and a lateral ridge contact in any desired depth by a two-stage epitaxial process. Completely processed TTG laser diodes with buried blocking regions exhibit very good high-temperature performance and a wavelength tuning range of around 4.5 nm under forward bias together with a maximum light output of as much as 25 mW at room temperature.

Narrow spectral linewidth 150mW semiconductor laser with fundamental transverse mode for SHG light source

A highly reliable, narrow spectral linewidth, 150 mW high-power semiconductor laser that oscillates at a wavelength of 860 nm has been developed, by optimising the structure with a 0.7 mu m thick p-cladding layer, a 900 mu m long cavity length, and current-blocking regions near the facets. Stable, fundamental transverse mode operation was obtained up to 230 mW. The spectral linewidth was 5 MHz at 150 mW. stable operation under 150 mW at 50 degrees C was confirmed for more than 2000 h.

Wide-stripe AlGaInP laser diodes with current-blocking region near facets grown on misoriented substrates

Wide-stripe high-power AlGaInP laser diodes (λL = 659 nm) with a current-blocking region (CBR) near the facets have been successfully fabricated for the first time by MOCVD using (100) GaAs substrates with a misorientation of 7° towards the (011) direction. The laser diodes show linear light output against current characteristics, in contrast with those fabricated using (100) substrates. Maximum continuous-wave light output power is achieved with 410 mW at 20°C.

High-power operation of 630 nm-band transverse-mode stabilised AlGaInP laser diodes with current-blocking region near facets

High-power type AlGaInP laser diodes (λL = 635 nm) with the current-blocking region near the facets have been successfully fabricated for the first time, by MOCVD using the (100) GaAs substrates with a misorientation of 5° towards the (100) direction. The maximum continuous wave output power was achieved with about 33 mW at 20°C. Fundamental transverse-mode operation was obtained up to 20 mW.

Extremely low threshold current operation in 1.5- mu m MQW-DFB laser diodes with semi-insulating InP current blocking region

Threshold current operation of 1.5 mA was achieved for 1.5- mu m multiple-quantum-well distributed feedback (MQW-DFB) laser diodes (LDs) with semi-insulating current blocking layers entirely grown by metalorganic vapor phase epitaxy (MOVPE). Such low-threshold current is attained by reducing leakage current and mirror loss in the laser structure. The required bias current for achieving several gigahertz bandwidth is markedly reduced due to the enhanced differential gain and low threshold current. Due to the reduced lasing delay time in such low threshold LDs, up to 5-GHz zero-bias current modulation, with a clear eye opening, is successfully demonstrated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Frequency characteristics of the Mn-doped InP p-n junction

Admittance spectroscopy is applied to the analysis of the thermal properties of the Mn acceptor-doped InP grown by liquid-phase epitaxy. The thermal activation energy and capture cross section are determined as ΔET=183 meV and σp=1.8×10−13 cm2, respectively. The cutoff frequency of the emission of holes from the Mn acceptor is 1 GHz at 300 K. It is shown that the small signal frequency characteristic of a buried heterostructure laser is improved at frequencies f&amp;gt;1 GHz by using the Mn-doped p-InP layer for the current blocking region.