Contact Resistance of InGaN/GaN Light Emitting Diodes Grown on the Production Model Multi-Wafer MOVPE Reactor
- PDF / 454,904 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 10 Downloads / 148 Views
wnloaded from https://www.cambridge.org/core. IP address: 91.243.90.240, on 09 Nov 2018 at 11:51:01, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/S1092578300003288
InGaN/GaN LEDs on multi-wafer MOVPE reactor with high thickness uniformity and the development of a self-aligned LED fabrication process that incorporates a thin current spreading layer. We also present detailed studies on the variation of contact resistance rc of Ni/Cr/Au on p-doped GaN layer versus annealing temperature. EXPERIMENT The InGaN/GaN LED samples were first grown on the Aixtron production model multi-wafer MOVPE reactor. The structures consist of 1.5 µm n-GaN layer, a thin InGaN quantum well (4-8 nm), and a 0.5 µm p-GaN cap layer, all grown on 2-inch (0001) sapphire substrates. The growth uses standard precursors including TMGa and TMIn for Group III and NH3 for Group V elements, and silane and MgCp2 are used for n-type and p-type dopant sources, respectively. The un-intentionally doped GaN is n-type with carrier concentration ~ 13x1017/cm3. The p-type GaN with hole concentration of ~5x1017/cm3 are routinely achieved after post-growth annealing. The thickness uniformity across the diameter of a 2-inch wafer was evaluated using spectral reflectometry measurement in the range of 670 to 1100 nm. Self-Aligned Ni/Au Current Spreading Layer
p - Contact
GaN:Mg
InGaN/GaN Quantum Well
GaN:Si
n - Contact GaN:Si
Sapphire
Fig. 1(a) The schematics of self-aligned InGaN/GaN LED structure. Note that a thin Ni/Au layer is deposited on top of the LED mesa to improve the current spreading.
Fig. 1(b) SEM of a typical LED structure with a magnified view of the edges of mesa after RIE etching.
The process flow for fabricating a LED with a structure shown in Fig. 1(a), is described as follows. First, a thin current spreading layer consists of Ni/Au (40 Å/40 Å) was deposited on the entire wafer using electron beam evaporation. The estimated optical absorption due to the current spreading layer is ~ 38% [4]. The sample is thermally annealed at 500oC under N2 ambient for 100 seconds. The LED mesa is then defined by a photoresist pattern. This is followed by ion milling to remove all except the current spreading layer, and Reactive Ion Etching (RIE) in a mixture of Cl2 and BCl3 to remove the GaN all the way to the n-layer. In this way, the current spreading layer and the mesa are formed in a self-aligned way. Figure 1(b) shows the SEM micrographs of the RIE etched surface around the LED mesa. Both the
Downloaded from https://www.cambridge.org/core. IP address: 91.243.90.240, on 09 Nov 2018 at 11:51:01, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/S1092578300003288
bottom and lateral surfaces of the etched mesa appear to be very smooth. Finally, Ni/Cr/Au (150 Å/150 Å/1200 Å) were e-beam evaporated to form both n and p-type contact pads. LEDs without current spreading layer are also fabricated for comparison. By
Data Loading...
