Sub-mount having photodiode and light-emitting element module

1. A sub-mount having a photodiode region, comprising:

a laser diode light-emitting element that emits light having an emission wavelength which changes as temperature changes within a range of −10° C. and 90° C.; and

a photodiode having a first conductivity-type layer arranged in a surface portion of the sub-mount in a photodiode region and configured to form a light-receiving surface, and having a second conductivity-type region arranged below the first conductivity-type layer, the photodiode being configured to receive at the light-receiving surface a light emitted from the light-emitting element and to convert the light into a photocurrent,

wherein the photodiode additionally has a depletion layer generated from the first conductivity-type layer, the depletion layer having a thickness in the range 20 μm to 45 μm; and

wherein a peak light-receiving wavelength at which the photocurrent of the photodiode becomes its maximum value is more than or equal to a minimum emission wavelength of the light-emitting element and less than or equal to a maximum emission wavelength of the light-emitting element.

2. The sub-mount of claim 1 , wherein the peak light-receiving wavelength of the photodiode is within ±5% of a median emission wavelength of the light-emitting element.

3. The sub-mount of claim 1 , wherein the photodiode is configured to receive the light whose emission wavelength ranges from 790 nm to 845 nm emitted from the light-emitting element.

4. The sub-mount of claim 1 , wherein the first conductivity-type layer has a depth of 1 μm to 5 μm.

5. The sub-mount of claim 1 , wherein the photodiode includes an i-type semiconductor layer interposed between the first conductive-type layer and the second conductive-type region.

6. The sub-mount of claim 1 , wherein the second conductivity-type region surrounds a periphery and a bottom portion of the first conductivity-type layer and wherein a portion of the second conductivity-type region is configured to form a portion of the surface of the sub-mount.

7. The sub-mount of claim 6 , wherein the photodiode includes a first electrode connected to the first conductive-type layer and a second electrode connected to the second conductive-type region, the first electrode and the second electrode being formed on the surface of the sub-mount.

8. The sub-mount of claim 1 , wherein the sub-mount is made of Si.

9. A light-emitting element module, comprising:

a laser diode light-emitting element that emits light having an emission wavelength which changes as temperature changes within a range of −10° C. and 90° C.,

a sub-mount comprising a photodiode having a first conductivity-type layer arranged in a surface portion of the sub-mount in a photodiode region and configured to form a light-receiving surface, and having a second conductivity-type region arranged below the first conductivity-type layer, the photodiode being configured to receive at the light-receiving surface a light emitted from the light-emitting element and to convert the light into a photocurrent,

wherein the light-emitting element is fixed on a surface of the sub-mount in a light-emitting element region adjacent to the photodiode region,

wherein the photodiode additionally has a depletion layer generated from the first conductivity-type layer, the depletion layer having a thickness in the range 20 μm to 45 μm, and

wherein a peak light-receiving wavelength at which the photocurrent of the photodiode becomes its maximum value is more than or equal to a minimum emission wavelength of the light-emitting element and less than or equal to a maximum emission wavelength of the light-emitting element.

10. The light-emitting element module of claim 9 , wherein the light-emitting element module includes a laser diode having a laser-emitting end surface and an opposite end surface opposite the laser-emitting end surface, the laser diode being arranged with the opposite end surface facing the light-receiving surface.

11. The light-emitting element module of claim 9 , wherein the light-emitting element module includes a light-emitting diode having a light-emitting surface, the light-emitting diode being arranged with the light-emitting surface facing upward.