This invention relates generally to semiconductor devices and more particularly to heterostructure semiconductor lasers.
Heterostructure semiconductor lasers have current blocking layers to isolate active regions of the laser. The most common approach to produce a current blocking layer for the buried heterostructure laser is to include extensive reversed biased p-n junctions to act as the blocking layer. However, extensive reversed biased p-n junctions have high capacitance characteristics that contribute to the total capacitance of the laser. The capacitance of the laser is one of the limiting factors for the rate of modulation in the active layer. To reduce this capacitance, isolation channels are often formed parallel to the active layer structure to reduce the size of the p-n regions. However, these isolation channels or trenches tend to inhibit heat removal from the active layer.
According to an aspect of the present invention, a method of fabricating a buried heterostructure semiconductor device includes producing a hybrid current confinement region adjacent to active layers of the device, by disposing a sequence of the p-n-p layers surrounding the active layer; and disposing a semi-insulating material around the p-n-p layers surrounding the active layers.
According to an additional aspect of the invention a semiconductor device includes a semiconductor substrate supporting an active region comprised of a multiple quantum well active regions and confinement layers having defined gratings and grating overgrowth regions to produce a laser device. The device also includes a current confinement layer including a sequence of doped n-p-n-p semiconductor layers to produce a n-p-n-p blocking structure and a semi-insulating semiconductor material over the n-p-n-p blocking structure.
One or more of the following advantages may be provided by one or more aspects of the invention.
The present invention introduces a hybrid current confinement for buried heterostructure (BH) semiconductor lasers. The hybrid current confinement structure includes a current blocking arrangement adjacent to the active layer. The current blocking arrangement is accomplished by a sequence of p-n-p-n layers. Further away from the active layer, a semi-insulating material (InP:Fe in this case) is used to provide current confinement for the active layer.
This arrangement has several advantages over existing approaches. The active layer is surrounded by a p-n-p-n layer sequence and therefore there is no inter-diffusion of dopants from the semi-insulating layer and active layer, e.g., Zn and Fe. This ensures a minimum of non-radiative centers in the active layer. The invention allows the lateral dimension (extent from the active layer) of the n-p-n-p blocking layers to be minimized. This results in a low parasitic capacitance of the laser and low leakage current. In some embodiments, the Fe doped semi-insulating material is grown last (nothing is grown on top of this layer), and hence the inter-diffusion of Zn and Fe is very limited. If inter-diffusion is present, it occurs away from the active region. The provision of the semi-insulating layer eliminates the need for isolation channels (trenches) parallel to the active layer to electrically isolate the active region. Isolation is now provided by the re-grown semi-insulating layer InP:Fe.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.