Abstract Liquid phase epitaxy is employed to grow a lattice matched layer of GaAsSb on GaAs substrates through the compositional intermediary of the III-V alloy system AlGaAsSb which acts as a grading layer. The Al constituent reaches a peak atomic concentration of about 6% within the first 2.5μm of the transition layer, then decreases smoothly to about 1% to obtain a lattice constant of 5.74 A. In the same interval the equilibrium concentration of Sb smoothly increases from 0 to about 9 atomic percent to form a surface on which a GaAsSb layer having the desired energy bandgap of 1.1 ev for one junction of an optimized dual junction photovoltaic device. The liquid phase epitaxy is accomplished with a step cooling procedure whereby dislocation defects are more uniformly distributed over the surface of the growing layer.
The method of lattice grading GaAsSb to GaAs by liquid phase epitaxy comprising the steps of forming a melt of Al, Ga, As, and Sb, the proportion of Sb to Ga being in the range greater than 0 to 4, the melt saturated with GaAs and the proportion of Al being in the range from 1 to 5×10 -3 atomic percent, heating said melt to the temperature of at least 830° C., contacting said GaAs with said melt, cooling the melt at a desired rate to a temperature lower than 770° C.
Claim 2
Independent Claim
92 words
The method of lattice grading GaAsSb to GaAs by liquid phase epitaxy comprising the steps of forming a melt of Al, Ga, As, and Sb, the proportion of Sb to Ga being in the range greater than 0 to 4, the melt saturated with GaAs and the proportion of Al being in the range from 1 to 5×10 -3 atomic percent, heating said melt to the temperature of at least 830° C., contacting said GaAs with said melt, cooling the melt at a desired rate to a temperature lower than 770° C.
Claim 3
Dependent Claim
26 words
The method of claim 1 wherein the step of cooling includes carrying out said cooling at a rate of less than approximately 0.5 C per minute.
Claim 4
Dependent Claim
49 words
The method of claim 2 wherein the step of cooling includes maintaining said rate for a desired temperature range and maintaining the melt at the lower temperature of said temperature range for a length of time sufficient for the distribution of dislocation defects over the surface of said layer.