No abstract

No abstract

We investigate colour‐coded InGaN‐based light‐emitting diodes (LEDs) where the position of a cyan‐emitting quantum well (QW) embedded into a blue‐emitting active region was varied systematically. The intensity ratio between the light output originating from the cyan and the blue QWs for different temperatures is analyzed both under electroluminescence (EL) and photoluminescence (PL) conditions. In EL, the contribution of the cyan QW increases when its position draws nearer to the p‐side. Surprisingly, a similar behaviour is also observed under PL excitation. Clear evidence of limited multi‐quantum‐well (MQW) operation at room temperature is found by comparing the relative emission intensities for different temperatures. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

No abstract

A method for improving adhesion between polymer films on Si substrates is described involving mechanical interlocking. Isotropic reactive ion etching (RIE) is applied to form pits in the Si substrate which fill upon application of a polymer via spinning. After curing, interpenetrating polymer lobes form a robust bond with the Si substrate. Adhesion improvements over films on smooth substrates are demonstrated qualitatively through prolonged immersion in heated 40% potassium hydroxide (KOH) solution, and quantitatively through peel tests. Strips of SU-8 on smooth substrates separate completely within minutes of immersion in KOH, whereas mechanically interlocked strips remain attached throughout. Tests reveal significant improvements to peel resistance for strips with interpenetrating lobes, due to a combination of crack deflection and physical restraint at the bond interface. Surprisingly, lobes with a vertical profile offer better resistance to strip peeling compared with lobes having significant overhang. Stress concentrations at sharp bends in the latter raise local stresses to levels promoting failure in SU-8, limiting the nominal load-carrying capacity of the interpenetrating interface. For maximum peel resistance, the lobe profile needs to be optimized such that maximum pull-out stresses are close to the failure stress of SU-8.