Devices distributed Bragg reflector

Eig. 3. Depiction of the light extraction, ie, escape cones of light emission, for various LED chip stmctures consisting of absorbing substrate devices having (a) thin window layers (top cone) (b) thick window layers (top cone and four one-half side cones) (c) thin window plus the implementation of a distributed Bragg reflector between the active layer and the substrate (top and bottom cone). Also shown is (d), the optimal stmcture for light extraction, a... 

Microcavity OLEDs fabricated on distributed Bragg reflectors (quarter wave stacks) [94]. Such OLEDs are fabricated on dielectric layers with significant dielectric contrast, so they narrow the emission spectrum by constructive interference. The narrow emission spectra also result in more efficient and more stable devices than regular OLEDs. The emission spectrum can be tailored to the specific sensor requirements (i.e., the absorption peak of the sensing element). 

Fig. 6.13 The microcavity, a vertical cavity lasing device, (a) Schematic depiction of the device, consisting of a distributed Bragg reflector, a PPV layer, and a silver layer.

Another device, the flexible distributed Bragg reflector laser with an active layer structure supporting second-order feedback, makes full use of the advantageous properties of polymers, namely flexibility, large-area fabrication, and low-cost processing [41, 42]. As can be seen in Fig. 6.15, the device consists of a one-dimensionally periodically structured flexible substrate coated with an m-LPPP layer, which acts as a planar wave guide. The substrate possesses a periodic height modulation with a period of A = 300 nm. 

The surface of the polymer layer exhibits a height modulation with the same period but a smaller amplitude (< 10 nm). It should be pointed out that the polymer layer in the device considered here functions as a distributed Bragg reflector and the... 

Fig. 6.15 Schematic illustration of a one-dimensionally patterned flexible distributed Bragg reflector laser device. Active layer 400 nm m-LPPP. Substrate 125 pm thick poly(ethylene terephthalate) film covered with acrylic coating. Adapted from Kallinger et al. [46] with permission from Wiley-VCH.

In recent years, semiconductor fabrication techniques have progressed to an extent that permits the construction of highly complex integrated devices such as the distributed Bragg-reflector (DBR) laser diode shown in Figure 7-9. This device contains a gallium arsenide /in-junction diode that produces infrared radiation at about 975 nm. In addition, a stripe of material... 

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