SPECTRAL AND ELECTRICAL CHARACTERISTICS OF P)-ALXGA1-XAS-P-AL(Y-GREATER-THAN-X)GA1-YAS-P-GAAS HETEROSTRUCTURES WITH ULTRATHIN SURFACE-LAYERS()

The dependences of the dark current-voltage characteristics and of the photoresponse spectra of n-GaAs-(n-p)-AlxGa1-xAs-p-Al(y>x)Ga1-yAs-p+- GaAs heterostructures on the composition of the photoactive layer (x=0 -0.7), on the thickness and composition of the wide-gap window layer o f p-type AlyGa1-yAs (D=0-300 angstrom, y=0.85-0.95), and on the thickn ess of the outer p+-type GaAs layer (d=0-300 angstrom) have been studi ed experimentally. It was established that the minimum values of the d ensity of the reverse dark currents j(d) almost-equal-to 10(-12) angst rom/cm were reached at x=0.3 (T=300 K) and the maximum values of the c ollection efficiency of photocarriers in the ultraviolet region (at la mbda=400 nm) amounted to Q(uv)=0.75 and were obtained for d, D=70 angs trom, y=0.95, and x=0. An increase in the ultraviolet sensitivity was in this case due to accumulation of a surface space charge in the heav ily doped p+-type GaAs layer and due to minimization of the losses ass ociated with the absorption of light in the wide-gap window and outer p+-type GaAs layers.