Investigation Of Zn Diffusion InⅢ-Ⅴ Compound Semiconductors And Fabrication Of Low Band-gap Infrared Cells

Zinc is a p-type dopant for semiconductors, zinc vapor phase diffusion process can be widely used for the P-type doping of III-V compound semicondutors such as GaSb, GaAs, GaP, InAs, etc. Therefore the investigation on the behavior of zinc diffusion in the above materials are important for device fabrication. However, zinc profiles in III-V compound semicondutors do not follow the complementary-error-function under the constant zinc surface concentration. Zinc profiles will show the kink-and-tail shapes with two diffusion fronts or the box shapes with a single diffusion front.We investigated the behaviors of zinc diffuion in GaSb, GaAs and InAs. For zinc diffusion in GaSb, we found that Ga atoms from diffusion sources suppressed the formation of the high-concentration surface diffusion regions in zinc profiles, thus converting the kink-and-tail-shaped profile into the box-shaped profile; our analysis demonstrated that both the surface and tail regions in the kink-and-tail profiles showed good regularities, the zinc diffusion coefficient (D) in the surface region is proportional to the square of the zinc concentration (C), that is D^C2; while there exits the relationship of D∝C in the tail region. The analysis revealed that the formation mechanism of the box profiles is the same as that of the tail region of the kink-and-tail profiles, the same PL signals related to the Ga excess were found in the above two regions, which demontrated that zinc atoms diffused through the kick-out mechanism.Our investigation found that the diffusion mechanism of zinc in GaAs is similar to that in GaSb, while it is different from that in InAs. Zinc diffusion profiles in InAs will show box shapes whether the pure zinc or Zn-In alloy were used as the diffusion sources. For the box profiles obtained under Zn-In sources, there exists the relations of D∝C in the whole region and will not appear the relation of D∝C-2in the shallow region.Sincethe formation of high-concentration surface diffusion regions can be suppresed by Ga atoms in diffuison sources, we proposed a sealed diffusion method using the Zn-Ga alloy sources to fabricate GaSb infrared cells. In the traditional fabrication process for GaSb cells, the pseudo-closed diffuison method using Zn-Sb alloy sources were used to prepare the PN junction. The zinc diffuison profiles will show kink-and-tail shapes with a surface high-concentration diffusion region before the kink point, the precise etching process were needed for etching the surface region to the kink point in order to improve the quantum efficiency of GaSb cells. However, it is difficult to realize pricise etching for the several hunred nanometers region. We used the sealed-quartz-tube diffuison method with Zn-Ga alloy sources to fabricate the PN junction of GaSb cells, which simplified the fabrication processes. The GaSb cells fabricated can maintain a stable electrical output performance, which is useful for volume production. The bandgap of InAs is lower than that of GaSb, thus the infrared cells manufactured using the InAs substrates can be used in a low-temperature thermophotovoltaic system.