Semiconductor laser

Wunstel, Klaus; Weinmann, Reinold;

In a semiconductor laser having a semi-insulating layer on the sides of a mesa to confine the current to the mesa during operation of the laser, at least one n-type layer and at least one p-type layer are provided above or below the semi-insulating layer.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor laser comprising at least one active region and at least one semi-insulating region on a semiconductor substrate, said at least one active region extending over part of the surface of the semiconductor substrate, and said at least one semi-insulating layer being disposed on both sides of the active region.

In Appl. Phys. Lett. 48 (1986), pp. 1572-1573, a DCPBH (double channel planar buried heterostructure) semiconductor laser is described which has four epitaxially grown layers on an n-InP substrate: an n-InP layer serving as a buffer layer and covering the n-InP substrate, an undoped InGaAsP layer serving as an active region, a p-InP layer serving as a waveguide region, and a p-InGaAsP layer serving as a contact layer.

Two parallel channels are etched into the InGaAsP, p-InP, and p-InGaAsP layers, leaving a mesa between them. The channels are filled with a semi-insulating layer which rises up to the level of the surface of the contact layer on the mesa at its sides. Atop the contact layer, the mesa has a metal contact to which a voltage is applied in operation.

Semi-insulating layers are less suited for current confinement than highly doped pn junctions. The latter, however, have a poor high-frequency response because of their high capacitance.

Semi-insulating layers have the disadvantage of becoming conductive at low voltages. Therefore, leakage currents flow during operation of the semiconductor laser.

SUMMARY OF THE INVENTION

It is the object of the invention to provide a semiconductor laser which has a very good high-frequency response and is suitable for high-speed optical communication.

This object is achieved by providing a semiconductor laser of the above kind in which on both sides of the active region, at least one n-type layer and one p-type layer are provided which are superimposed one upon another.

The semiconductor laser according to the invention has the advantage of delivering high output power.

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BRIEF DESCRIPTION OF THE DRAWING

Two embodiments of the invention will now be described with reference to the accompanying drawing, in which:

FIG. 1 is a cross section of a semiconductor laser with one semi-insulating layer, and

FIG. 2 is a cross section of a semiconductor laser with two semi-insulating layers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The semiconductor laser shown in FIG. 1 has a semiconductor substrate 1 of either a II-VI compound or a III-V compound, e.g., n-InP. The substrate 1 supports an active region 2 of InGaAsP, over which a waveguide region 3 of p-InP and a contact layer 12 of p-InGaAsP are provided.

The lasers 2, 3, 12 form a mesa which extends in the longitudinal direction of the semiconductor substrate 1.

On the sides of the mesa, several layers of InP lie on top of one another: a semi-insulating layer 4, a p-type layer 5, an n-type layer 6, a p-type layer 7, and an n-type layer 8. The layer 8 and the contact layer 12 form a common planar surface. The layer 8 is covered by a layer 9 of silicon dioxide; the layers 9 and 12 are covered by a metal layer 10, which serves as a contact layer. The underside of the semiconductor substrate 1 is covered by a metal layer 11, which serves as another contact layer.

Another embodiment of the semiconductor laser, shown in Fig. 2, has the same layers 1 to 3 and 9 to 12 as the semiconductor laser of FIG. 1.

On the sides of the mesa, a p-type layer 13, an n-type layer 14, a first semi-insulating layer 15, another p-type layer 16, another n-type layer 17, and a second semi-insulating layer 18 are superimposed one upon another.

Other sequences of semi-insulating and n- and p-type layers are also possible. If only a single semi-insulating layer is present, it may be located either below or above the n- and p-type layers.

Semi-insulating and n- and p-type layers lying on top of one another on the sides of an active region are suitable both for BH lasers and for TJS (transverse junction stripe) and CSP (channeled substrate planar) laers.