JPH0797659B2 - SiC blue light emitting diode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a SiC blue light emitting diode.

(B) Conventional technology 6H-SiC has attracted attention as a material for blue light emitting diodes because of its large bandgap and pn dual conductivity type.

The light emitting layer of the blue light emitting diode made of 6H-SiC is
Report by L. Heffmann et al. (Journal of Applied Physics
53 (10), 6962, (1982)), it is known that light is emitted in the n-side epitaxial growth layer by measurement using cathodoluminescence. Furthermore, a report by Gnther Ziegler et al. (IEEE Trans, Electron Devices, ED-30,277
(1983)), comparing aluminum-doped p-type 6H-SiC and undoped n-type 6H-SiC, it is described that aluminum-doped p-type 6H-SiC has a considerably lower transmittance.

From these points, as a structure of a SiC blue light emitting diode, as shown in FIG. 3, generally, a p-type 6H-SiC substrate (1) is a p-type 6H-doped with aluminum (Al).
A SiC layer (2) and an n-type 6H-SiC layer (3) doped with aluminum and nitrogen (N) are sequentially laminated, and the first and second layers are formed on the back surface of the substrate (1) and the n-type SiC layer (3). It is known that two ohmic electrodes (4) and (5) are formed.

(C) Problems to be Solved by the Invention However, there is a problem that such a homojunction SiC light emitting diode has low luminous efficiency.

As a result of diligent research on such a cause, as shown in the energy diagram of FIG. 4, in the homojunction described above, the junction (6) when a forward bias is applied becomes a gentle junction, and thus the actual light emitting region becomes n. The carrier high density state is unlikely to occur in the vicinity of the junction of the type 6H-SiC layer (3).
Regeneration of electrons (11) and holes (12) generated between the donor level (7) and the acceptor level (8) or between the conduction band (9) and the acceptor level (8) in the C layer (3). It was found that this was because the coupling efficiency was low.

In FIG. 4, (10) indicates a valence band, and the donor level (7) and the acceptor level (8) are impurity levels formed by nitrogen and aluminum, respectively.

(D) Means for Solving the Problems The present invention has been made in view of the above point, and its structural feature is that a 6H-SiC layer of one conductivity type is 4H that exhibits the same conductivity type as the layer.
The -SiC layer and the 4H-SiC layer have an opposite conductivity type to the 4H-SiC layer.

(E) Action In such a structure, when a forward bias is applied, the density of electrons and holes becomes high in the 6H-SiC layer.

(F) Example FIG. 1 shows a first example of the present invention. A p-type 4H—SiC layer (12) doped with aluminum and a aluminum- and nitrogen-doped p-type 4HSiC substrate (11). N-type 6H-
SiC layer (13) and nitrogen-doped n-type 4H-SiC layer (1
4) Sequential stacking and backside of substrate (11) and p-type 4H-S
Ohmic first and second electrodes (15) on the iC layer (14)
(16) is formed.

2 (a) and 2 (b) show the P-type 4H4SiC layer (1
2) shows the energy states of the n-type 6H-SiC layer (13) and the n-type 4H-SiC layer (14). Specifically, FIG. 2 (a) shows the energy state at the time of thermal equilibrium, and FIG. (B) shows the energy states when a forward bias is applied.

As shown in FIG. 2 (a), the p-type 4H-SiC layer (12) and n
The band gap of the type 4H-SiC layer (14) is about 3.27 eV, and n
The band gap of the type 6H-SiC layer (13) is about 3.02 eV. Therefore, when a forward bias is applied, as shown in FIG. 2 (b), the conduction band (18) of the junction (17) between the n-type 6H-SiC layer (13) and the p-type 4H-SiC layer (12). Side and n-type 4H-SiC layer (14)
Valence band (2) of the junction (19) between the n-type 6H-SiC layer (13) and
Barriers (21) and (22) with a height of about 0.2 eV are generated on the 0) side, respectively.
Therefore, from the n-type 6H-SiC layer (13) to the p-type 4H-SiC layer (1
Most of the injection of electrons (23) into the 2) and injection of holes (24) from the n-type 6H-SiC layer (13) into the n-type 4H-SiC layer (14) are caused by the barriers (21) ( 22). At this time, the n-type 4H-SiC layer (14) and the n-type 6H-SiC layer (13) are connected to the conduction band (18) side of the junction (19) and the n-type 6H-SiC layer (13).
Valence band (2) of the junction (17) between the p-type 4H-SiC layer (12) and
Barriers (25) and (26) also occur on the 0) side, respectively, but since the barriers (25) and (26) are very low, the n-type 4H-SiC layer (14)
Injection of electrons (23) from the n-type 6H-SiC layer (13) and p
The holes (24) are efficiently injected from the type 4H-SiC layer (12) to the n-type 6H-SiC layer (13).

As a result, in the device of this embodiment, in the n-type 6H—SiC layer (13), the electron (23) located at the conduction band (18) or the donor level (27) and the hole (24) located at the acceptor level (28). And are recombined, and light with energy hv ≈ 2.6 eV, that is, wavelength 4
It will emit blue light of 80 nm. In addition, at this time, electrons (2) to the p-type 4H-SiC layer (12) are generated by the barriers (21) (22).
Since the injection of 3) and the injection of holes (24) into the n-type 4H-SiC layer (14) are blocked, electrons (23) and holes (24) are contained in the n-type 6H-SiC layer (13). ) Is a high density area. Therefore, in such an n-type 6H-SiC layer (13), recombination efficiency of electrons (23) and holes (24) is improved as compared with the vicinity of the junction (6) of the conventional device of FIG. As a result, the luminous efficiency is also improved.

In FIG. 2, the donor level (27) and the acceptor level (28) are levels formed by nitrogen or aluminum doped as impurities, respectively.

In addition, although the 6H—SiC layer (13) is of the n-type in this example, it was confirmed by experiments that the same effect can be obtained by using the p-type. Furthermore, in order to increase the efficiency of carrier injection into the layer (13), the layer (13) may be of n-type or p-type.

(G) Effect of the Invention According to the present invention, the density of carriers in the region where electrons and holes are recombined can be increased, so that blue light can be generated with higher efficiency than ever before.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are schematic views showing an energy state of the present embodiment,
FIG. 3 is a sectional view showing a conventional example, and FIG. 4 is a schematic diagram showing an energy state of the conventional example. (12) …… p-type 4H-SiC layer, (13) …… n-type 6H-SiC layer,
(14) ... n-type 4H-SiC layer.

Claims (1)

[Claims] 1. A 6H-SiC layer of one conductivity type, a 4H-SiC layer having the same conductivity type as the layer, and a 4H-SiC layer having a conductivity type opposite to that of the 4H-SiC layer.
A SiC blue light-emitting diode characterized by being equipped with a SiC layer.