652
23 Electricity-to-Light Conversion
(a)
(b)
Fig. 23.12 a Scheme of thin-film flip-chip LED with microprisms. b image and luminescence image of thin film AlInGaP
LED (chip length: 320 µm). Reprinted with permission from [1951]
(a)
n-GaN
p-GaN
active
InGaN
MQW
metal anode
ceramic submount
metal cathode
(b)
Fig. 23.13 a Scheme of thin-film flip-chip LED with rough surface and contacts from one side. b Emission image of
1 × 1 cm 2 chip. Adapted from [1952]
Fig. 23.14 Triangular
GaN LED chip with high
extraction efficiency. Both
the p- and n-contact are on
the bottom. Adapted
from [1943]
image are shown. Here, the n-contact runs through a via hole with insulated side walls. In the emission
image the array of via holes can be seen.
Bulk Flip-Chip
In the GaN material system a LED based on a triangular chip with 400 µm side length using a bulk
substrate with 150 µm thickness has been presented that exhibits the so far highest extraction efficiency
of almost 90% (Fig.23.14) [1943, 1953]. The top and all side facets are rough.
Cascaded LEDs
Similar to the use of tunneling junctions in multi-junction solar cells (Sect. 22.4.6), the monolithic
serial connection of several LED layers has been proposed [1954] (Fig. 23.15). For a given output
power P at forward voltage V F and current density j of a single junction LED, ideally a LED with N
identical stacks and N − 1 tunneling junctions provides the same output power P at the N -fold forward
voltage, as reported for N = 2, 3 in [1955], and the current density j/N . Since the internal quantum
23 Electricity-to-Light Conversion
(a)
(b)
Fig. 23.12 a Scheme of thin-film flip-chip LED with microprisms. b image and luminescence image of thin film AlInGaP
LED (chip length: 320 µm). Reprinted with permission from [1951]
(a)
n-GaN
p-GaN
active
InGaN
MQW
metal anode
ceramic submount
metal cathode
(b)
Fig. 23.13 a Scheme of thin-film flip-chip LED with rough surface and contacts from one side. b Emission image of
1 × 1 cm 2 chip. Adapted from [1952]
Fig. 23.14 Triangular
GaN LED chip with high
extraction efficiency. Both
the p- and n-contact are on
the bottom. Adapted
from [1943]
image are shown. Here, the n-contact runs through a via hole with insulated side walls. In the emission
image the array of via holes can be seen.
Bulk Flip-Chip
In the GaN material system a LED based on a triangular chip with 400 µm side length using a bulk
substrate with 150 µm thickness has been presented that exhibits the so far highest extraction efficiency
of almost 90% (Fig.23.14) [1943, 1953]. The top and all side facets are rough.
Cascaded LEDs
Similar to the use of tunneling junctions in multi-junction solar cells (Sect. 22.4.6), the monolithic
serial connection of several LED layers has been proposed [1954] (Fig. 23.15). For a given output
power P at forward voltage V F and current density j of a single junction LED, ideally a LED with N
identical stacks and N − 1 tunneling junctions provides the same output power P at the N -fold forward
voltage, as reported for N = 2, 3 in [1955], and the current density j/N . Since the internal quantum