Current spreading layers

Current-spreading layers, in light emitting diodes, 14 840... 

In LEDs with thin top confinement layers, the current is injected into the active region mostly under the top electrode. Thus, light is generated under an opaque metal electrode, which results in a low extraction efficiency. The problem can be avoided with a current-spreading layer or window layer that spreads the current under the top electrode to regions not covered by the opaque top electrode. 

For circular contact geometry, the thickness of the current spreading layer, t, results a current-spreading length Ls given by [32]... 

During epitaxial growth, the semiconductor layers must be doped to form thep—n junction and conductive current spreading window layers. Eor III—V materials, zinc, Zn beryUium, Be carbon, C magnesium. Mg and siUcon, Si are commonly employed as -type dopants, whereas tellurium, Te ... 

Fig. VII-1 shows a schematic of the structure of a polymer LED and a picture of a thin film flexible polymer LED seven-segment display. The bottom electrode of this display was made by spin-cas ting a layer of metallic polyaniline onto a flexible plastic substrate [69]. Polyaniline was chosen as the electrode material because it is flexible, conducts current, and is transparent to visible light. The emissive layer of the display was fo med by spin casting a layer of MEH-PPV over the polyaniline. The top electrodes were formed by evaporating calcium through a patterned shadow mask. Since the conductivity of undoped emissive polymers is relatively low, it was not necessary to pattern the polymer or the bottom electrode to prevent current spreading between neighboring pixels.

The schematic structure of an ODR-based LED a shown in Fig. 1.19. It consists of a top current-spreading (or window) layer, the active and confinement layers, a bottom window layer, the ODR, and a submount such as a Si or metal wafer. The active layers include the lower and upper confinement layers and the bulk or multiple-quantum-well (MQW) active region. The wafer is grown in the standard p-side up mode that is employed in nearly all LEDs at the present time. 

Spill Anatomy and Remediation. Contrary to past arguments that leaks or spills from aboveground tanks would stay near the surface, they go straight down into the aquifer and spread out. Various obstacles, such as clay lenses, rock, or impermeable layers of sod, simply divert the downward path. Slow leaks from tank bottoms tend to form a narrow plume, whereas larger spills cover much wider areas. When the contaminant reaches groundwater, it tends to be dispersed in the direction of the groundwater current and movement. 

Downward flame spread for scenario B. Once the horizontal, concurrent flame spread along the wall ceiling intersection has reached an opposite corner in the compartment the downward flame spread in the upper layer starts. In reality, this could possibly start happening during the concurrent flame spread time interval. In the current version of the model, no account is taken of the relatively low oxygen concentration in the upper layer. The flame spread is quite slow at first since the wall material has a relatively low sur-... 

As may be imagined, the ordinary burner, as nsed for sulphur alone, lately described, is not adapted to bum pyrites a burner of peculiar construction is required. The burner for this purpose is, in general structure, not unlike a lime-kiln. In the case of burning sulphur itself, the object is to spread a layer on a flat plate, so that, when fused and burning, it exposes a large surface for the current of air to sweep over this js necessary on account of the fusion of the sulphur. But pyrites does not fuse except at a very high heat, The pieces retain their shape and as it is imperative that they shall attain a red heat, it is necessary to bum. them in eubh a manner that amass of them oan be kept together. 

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