Epitaxial wafer, light-emitting element, method of fabricating epitaxial wafer and method of fabricating light-emitting element

• US 8,212,268 B2
• Filed: 01/25/2010
• Issued: 07/03/2012
• Est. Priority Date: 09/04/2009
• Status: Expired due to Fees

• Current Assignee: Sumitomo Chemical Company Limited
• Original Assignee: Hitachi Cable Limited (Proterial Ltd.)
• Inventors: Konno, Taichiroo
• Primary Examiner(s): Weiss, Howard
• Assistant Examiner(s): Ingham, John C
• Application Number:
  US12/692,754
• Publication Number:
  US 20110057214A1
• Time in Patent Office: 890 Days
• Field of Search: 257/94, 257/95, 257/E33.069, 257/97, 438/38
• US Class Current: 257/95
• CPC Class Codes: H01L 33/10 with a light reflecting structure, e.g. semiconductor Bragg reflector
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers

Abstract

An epitaxial wafer, a light-emitting element, a method of fabricating the epitaxial wafer and a method of fabricating the light-emitting element, which have a high output and a low forward voltage, and can be fabricated without increasing fabricating cost, are provided. The epitaxial wafer is formed with a light-emitting portion, a reflective portion provided between a semiconductor substrate and the light-emitting portion and a current dispersing layer having first and second current dispersing layers, wherein the reflective portion has plural pairs of layers having first and second semiconductor layers wherein the first semiconductor layer has a thickness of T_A defined by Equation (1),

$\begin{array}{cc}{T}_A=\frac{{\lambda }_p}{4n_A\sqrt{1-{\left(\frac{n_{In}\sin \theta }{n_A}\right)}^2}}& \left(1\right)\end{array}$
the second semiconductor layer has a thickness of T_B defined by Equation (2),

$\begin{array}{cc}{T}_B=\frac{{\lambda }_p}{4n_B\sqrt{1-{\left(\frac{n_{In}\sin \theta }{n_B}\right)}^2}}& \left(2\right)\end{array}$
and the second current dispersing layer has a high carrier density or a high impurity density and is provided with the convexoconcave portion on the surface.

Claims

1. An epitaxial wafer, comprising:

a semiconductor substrate;

a light-emitting portion including an active layer provided between a first cladding layer of a first conductivity type and a second cladding layer of a second conductivity type different from the first conductivity type;

a reflective portion which is provided between the semiconductor substrate and the light-emitting portion and which reflects a light emitted from the active layer; and

a current dispersing layer provided on an opposite side of the reflective portion in relation to the light-emitting portion, and including first and second current dispersing layers having different carrier densities and impurity densities from each other,

wherein the reflective portion includes plural pairs of layers each including a first semiconductor layer and a second semiconductor layer different from the first semiconductor layer,

wherein the first semiconductor layer has a thickness of T_A defined by Equation (1),

2. The epitaxial wafer according to claim 1, wherein the reflective portion comprises at least three pairs of layers,

wherein a thickness of each pair of layers is different from each other according to differences of θ

in Equations (1) and (2) for each pair of layers,

wherein at least one pair of layers includes first and second semiconductor layers which are defined by a value of θ

larger than 50°

.

3. The epitaxial wafer according to claim 2, further comprising:

an intermediate layer provided between the second cladding layer and the current dispersing layer,

wherein the intermediate layer is formed from a semiconductor having a bandgap energy between that of a semiconductor composing the second cladding layer and that of a semiconductor composing the current dispersing layer.

4. The epitaxial wafer according to claim 3, wherein the first and second semiconductor layers are transparent to a light emitted from the active layer, and comprising an AlGaAs based semiconductor which has a larger bandgap energy than that of a semiconductor composing the active layer,

wherein an Al composition of the semiconductor layer composing the first semiconductor layer is different from that of the second semiconductor composing the second semiconductor layer.

5. The epitaxial wafer according to claim 4, wherein one of the first and second semiconductor layers of a pair of layers positioned firstly in the reflective portion relative to the semiconductor substrate or one of the first and second semiconductor layers of pairs of layers positioned firstly and secondly therein relative to the semiconductor substrate are formed from a semiconductor material which is opaque to the light emitted from the active layer, or are formed from a semiconductor material having a smaller bandgap energy than that of the active layer.

6. The epitaxial wafer according to claim 5, wherein

the intermediate layer includes Ga_zIn_1-zP(0.6≦

z≦

0.9).

7. A light-emitting element, comprising:

the epitaxial wafer defined in claim 1;

a front surface electrode provided on the second current dispersing layer; and

a back surface electrode provided on an opposite side of the reflective portion in relation to the semiconductor substrate.

8. The light-emitting element according to claim 7, comprising:

a light-extracting layer on a surface of the second current dispersing layer in a region excluding the front surface electrode,

wherein a material composing the light-extracting layer is transparent to a light emitted from the active layer and has a refractive index between that of semiconductor composing the second current dispersing layer and that of air.

9. The light-emitting element according to claim 8, wherein

the light-extracting layer has a thickness of d within ±

30% of a value defined by A×

λ

_p/(4×

n), wherein λ

_p is a wavelength of a light emitted from the active layer, n is a refractive index of the light-extracting layer and A is a constant (A is an odd number).

10. A method of fabricating an epitaxial wafer comprising:

growing a reflective portion, formed on a semiconductor substrate, including plural pairs of layers having a first semiconductor layer and a second semiconductor layer different from the first semiconductor layer;

growing a light-emitting portion, formed on the reflective portion, including an active layer provided between a first cladding layer of a first conductivity type and a second cladding layer of a second conductivity type which is different from the first conductivity type;

growing a current dispersion layer, formed on the light-emitting portion, including first and second current dispersing layers which have different carrier densities or impurity densities each other; and

forming a convexoconcave portion on a surface of the second current dispersing layer,

wherein the first semiconductor layer has a thickness of T_A defined by Equation (1),

11. A method of fabricating a light-emitting element comprising:

growing a reflective portion comprising plural pair of layers, formed on a semiconductor substrate, including a first semiconductor layer and a second semiconductor layer different from the first semiconductor layer;

growing a light-emitting portion, formed on the reflective portion, including an active layer provided between a first cladding layer of a first conductivity type and a second cladding layer of a second conductivity type which is different from the first conductivity type;

growing a current dispersion layer, formed on the light-emitting portion, including a first and second current dispersing layers which have different carrier densities or impurity densities each other;

forming a convexoconcave portion on a surface of the second current dispersing layer;

forming plural front surface electrodes on a surface of the second current dispersing layer after the forming step of the convexoconcave portion, and

cutting each region among the plural front surface electrodes,

wherein the first semiconductor layer has a thickness of T_A defined by Equation (1),